Information

Moss Transportation System


In my biology textbook, it says that mosses are avasculer and do not have xylem like spermatophytes. So by what means do mosses transport nutrients ?


Mosses are able to transport water and nutrients internally through intercellular voids and cell-to-cell connections involving exchanges of cytoplasm, as well as externally across their surface. Labeling mosses as nonvascular plants is misleading because mosses in the Polytrichales order have highly specialized water and nutrient conducting systems which are reminiscent of xylem and phloem. But in general, a moss's main vascular system can be said to be its outer surface which is carefully designed to store and conduct water across the plant.

External Conduction

Moss cells absorb water and nutrients directly from their environment, so many of their nutritional needs can be met simply by ensuring water and its dissolved nutrients can spread across the entire surface of the moss plant. The water is able to spread through capillary action, aided by a carefully designed surface. Moss leaves are frequently appressed to the stem and have sheathed bases which create small places for water to climb along a stem. The leaves may also be covered in small bumps (papillae) which create capillary spaces. Rhizoids, which are somewhat like roots except typically only 1 cell thick, can also make good paths for water to flow across. Some mosses have their stems covered in rhizoids or paraphyllia to help conduct water. Sphagnum mosses have large cells across their leaves which exist mainly to absorb water like a sponge, and Leucobryum mosses have a layer of water holding cells on both sides of their leaves. Colonies of mosses often form compact mounds that allow for water to flow across the entire mound.

As far as I know, moss cells do not deliberately dump nutrients into the film of water on their surface in the hopes that it will be absorbed by other cells of the plant that need it more. But, when dessicated moss is rehydrated, solutes in the protoplasm may leak into the external film of water. These contents might be able to be reabsorbed by other cells of the moss, forming an incidental external nutrient transport pathway.

Internal Conduction

Water and nutrients are also able to flow through cells or spaces between cells from inside the moss. Experiments have shown that nutrients are relocated from old growth to new growth using cytoplasm-linked pathways in Sphagnum and Polytrichaceae mosses. Many moss stems and almost all seta (the stalk connecting a spore capsule to the main body of the parent moss plant) have special nutrient conducting parenchyma cells surrounding water conducting cells called hydroids. The central ribs of moss leaves also often show a similar pattern. Sometimes these chains of nutrient conducting cells in the leaves connect to the main conducting strands in the stem, but usually the leaf conducting strands come to an end somewhere in the stem cortex without connecting.

Mosses in the Polytrichales order have the most specialized nutrient and water conducting cells of all mosses. The nutrient conducting cells for mosses in this order are different enough from other mosses to be given a special name--leptoids. The vascular system in these mosses are not evolutionarily homologous to xylem and phloem, but serve the same basic transport purpose. In Polytrichum moss, water has been measured to flow 200 cm/h through the stem and organic compounds at 32 cm/h. These specialized hydroids and leptoids are what enables the tallest moss, Dawsonia superba, to grow up to 70 cm.

The water and nutrient transport architecture for mosses outside the Polytrichales is more variable and less specialized. Andreaeopsida, Andreaeobryopsida, and Sphagnopsida completely lack hydroids. Takkakia's hydroids are unique in that they are short instead of tall and transfer water through pores formed from plasmodesmata at their ends. Sphagnum has nutrient conducting cells, but they are not homologous to the nutrient transferring parenchyma cells of other mosses. Some mosses in families which typically have central conducting strands have lost that feature over time, and mosses which would normally have hydroids may fail to develop them if grown underwater.

Outside of the usual stem, seta, and leaf midrib conducting cells, it has been suggested that rhizoids and caulonemal cells also conduct nutrients due to similarities in cell organization to the nutrient conducting parenchyma cells. The cells that form the interface between the parent gametophyte and the sporophyte foot also transfer nutrients.

Sources

Chopra, R. N. Biology of Bryophytes. 2005. Chapter 11 "Conduction in Bryophytes".

Goffinet, B., and A. J. Shaw. Bryophyte Biology. 2009. Pages 60-70, 83, 301.

Ligrone, Duckett, and Renzaglia. Conducting tissues and phyletic relationships of bryophytes. 2000.


Moss Transportation System - Biology

Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta ( / b r aɪ ˈ ɒ f ɪ t ə / , [3] / ˈ b r aɪ . oʊ f aɪ t ə / ). Bryophyta is now the formal name for mosses alone, whereas "bryophyte" refers to the informal group of liverworts, mosses and hornworts. Mosses typically form dense green clumps or mats, often in damp or shady locations. The individual plants are usually composed of simple leaves that are generally only one cell thick, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Although some species have conducting tissues, these are generally poorly developed and structurally different from similar tissue found in vascular plants. [4] Mosses do not have seeds and after fertilisation develop sporophytes with unbranched stalks topped with single capsules containing spores. They are typically 0.2–10 cm (0.1–3.9 in) tall, though some species are much larger. Dawsonia, the tallest moss in the world, can grow to 50 cm (20 in) in height. There are approximately 12,000 species. [2]

Mosses are commonly confused with liverworts, hornworts and lichens. [5] Mosses were formerly grouped with the hornworts and liverworts as "non-vascular" plants in a division, all of them having the haploid gametophyte generation as the dominant phase of the life cycle. This contrasts with the pattern in all vascular plants (seed plants and pteridophytes), where the diploid sporophyte generation is dominant. Lichens may superficially resemble mosses, and sometimes have common names that include the word "moss" (e.g., "reindeer moss" or "Iceland moss"), but they are not related to mosses. [5] : 3

The main commercial significance of mosses is as the main constituent of peat (mostly the genus Sphagnum), although they are also used for decorative purposes, such as in gardens and in the florist trade. Traditional uses of mosses included as insulation and for the ability to absorb liquids up to 20 times their weight.


Physcomitrella patens, a versatile synthetic biology chassis

During three decades the moss Physcomitrella patens has been developed to a superb green cell factory with the first commercial products on the market. In the past three decades the moss P. patens has been developed from an obscure bryophyte to a model organism in basic biology, biotechnology, and synthetic biology. Some of the key features of this system include a wide range of Omics technologies, precise genome-engineering via homologous recombination with yeast-like efficiency, a certified good-manufacturing-practice production in bioreactors, successful upscaling to 500 L wave reactors, excellent homogeneity of protein products, superb product stability from batch-to-batch, and a reliable procedure for cryopreservation of cell lines in a master cell bank. About a dozen human proteins are being produced in P. patens as potential biopharmaceuticals, some of them are not only similar to their animal-produced counterparts, but are real biobetters with superior performance. A moss-made pharmaceutical successfully passed phase 1 clinical trials, a fragrant moss, and a cosmetic moss-product is already on the market, highlighting the economic potential of this synthetic biology chassis. Here, we focus on the features of mosses as versatile cell factories for synthetic biology and their impact on metabolic engineering.

Keywords: Biopharmaceutical Bioreactor Fragrance Gene targeting Genome engineering Green cell factory Photobioreactor.


Moss Plants and More

Here is a photo demonstration of the height difference between mosses and other plants such as trees. The mosses are in the foreground mixed in amongst the grass. They measure in at about 6 centimeters or so tall. Whereas the trees in the background are over 10 meters (1,000cm) tall.

The answer is Water. Water is one of the required elements for plants to carry out photosynthesis and live. Plants such as trees absorb water through their root systems and then transport the water to their leaves, the site of photosynthesis, through conducting cells. The cells that move water from the roots to the leaves are called xylem cells. These cells are dead at maturity and are very tough. They are the type of plant cell that composes wood. The substance that adds to the strength of these cells and makes them retain water to function as internal plant piping is a compound called lignin.

Mosses however do not have lignin in any of their cell walls and they do not have xylem cells either. Thus mosses do not have an efficient system for transporting water within their body long distances. Mosses absorb all of their water from the outside environment directly through their leaves and stem. (Imagine drinking through your skin.) Most plants must be small in order to keep their entire body hydrated and thus are limited in the height to which they can grow while still maintaining wet leaves. Also without the strength that xylem cells provide a very tall moss would be super flimsy. It would be like trying to build a tree out of wet spaghetti noodles. Quite the difficult task. Mosses have thus maintained a small stature for millions of years and despite the time have not gotten any taller.

2 comments:

I'm sure you noticed the double posting Jessica, but in case you hadn't, a heads up.

Also, when using the Read More feature, make sure you copy and paste in your text not using compose mode, but in edit html mode instead. That way you can keep track of the span tags. Looks like you might have figured that out however. :D

Thanks for the heads up about the double post. I was running out the door to go to pottery class and did not notice that it had loaded twice.

As for the read more feature it took me a while to get the hang of it. I am not html code savvy and I definitely had some frustrated yelling at the computer screen moments. I think that I have the hang of it now, but thanks for the advice. :)


Moss Transportation System - Biology

Starr's Biology Today and Tomorrow

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Biodiversity (Rediscovering Biology)

Dilution Effect: As suburbs developed in New England, the forest habitat became more patchy, resulting in the disappearance of some species and the proliferation of mice -- which are the reservoir for the Lyme spirochete -- and ticks, which carry the disease to humans. This increased the proportion of infected ticks, and led to an increase in human disease. Mass Extinctions: A graph showing the five major recognized mass extinctions over the last 600 million years. Trilobites went extinct at the end of the Permian era, while dinosaurs were casualties of the most recent mass extinction at the Cretaceous/Tertiary period border. Species Richness vs. Lyme Disease: Ostfeld's study found that as species richness declined, the incidence of Lyme disease increased. Test Strip - Cedar Creek: Each year, David Tilman collects the plant matter from a strip 10 cm by 3 m from each of his experimental plots to examine the effects of species diversity on biomass. Tilman's Experimental Plots: Tilman compares plots with few species (on left) to those with more species (as on the right). He has found that more diverse plots recover from disturbances like drought more quickly than those with fewer species.


The Bezanilla Lab

The major focus of our research is to understand how plant cells grow. We use the moss Physcomitrella patens as a model system and we employ many different tools, ranging from imaging to molecular engineering to get at this question.

How plant cells grow, one of the most fundamental aspects of plant biology, remains an open question. Our research focuses on understanding how proteins within the cell direct and regulate plant cell growth and morphogenesis. We are particularly interested in the role of regulators of the filamentous actin cytoskeletal network and have pioneered the use of the moss Physcomitrella patens to show that regulators of actin dynamics are critical for proper cell growth.

Among plants, moss has exceptionally rapid transgenic capabilities and is the only known land plant that undergoes efficient homologous recombination. My lab has developed additional tools, such as RNA interference (RNAi), quantitative complementation analyses, and rapid quantitative growth assays, which will enable a molecular characterization of plant cell growth.

The ultimate goal of our research is to use directed and undirected approaches to uncover the molecular basis of cell growth. As a basic understanding emerges from these functional genomic studies, it may be possible to manipulate attributes of other plants. For example, gene discovery for increased plant biomass may support new and innovative renewable energy sources.

Recent studies in the lab have lead to a working model for how tip growth in moss cells is controlled at the molecular level. We hypothesize that actin dynamics are required to establish and maintain an apical cortical F-actin structure that is required for transport of exoctyic vesicles delivering new growth material to the apex of the cell.


Phylum Lycopodiophyta: Club Mosses

The club mosses , or phylum Lycopodiophyta , are the earliest group of seedless vascular plants. They dominated the landscape of the Carboniferous, growing into tall trees and forming large swamp forests. Today’s club mosses are diminutive, evergreen plants consisting of a stem (which may be branched) and microphylls ([link]). The phylum Lycopodiophyta consists of close to 1,200 species, including the quillworts (Isoetales), the club mosses (Lycopodiales), and spike mosses (Selaginellales), none of which are true mosses or bryophytes.

Lycophytes follow the pattern of alternation of generations seen in the bryophytes, except that the sporophyte is the major stage of the lifecycle. The gametophytes do not depend on the sporophyte for nutrients. Some gametophytes develop underground and form mycorrhizal associations with fungi. In club mosses, the sporophyte gives rise to sporophylls arranged in strobili, cone-like structures that give the class its name. Lycophytes can be homosporous or heterosporous.



Lysosome biology in autophagy

Autophagy is a major intracellular degradation system that derives its degradative abilities from the lysosome. The most well-studied form of autophagy is macroautophagy, which delivers cytoplasmic material to lysosomes via the double-membraned autophagosome. Other forms of autophagy, namely chaperone-mediated autophagy and microautophagy, occur directly on the lysosome. Besides providing the means for degradation, lysosomes are also involved in autophagy regulation and can become substrates of autophagy when damaged. During autophagy, they exhibit notable changes, including increased acidification, enhanced enzymatic activity, and perinuclear localization. Despite their importance to autophagy, details on autophagy-specific regulation of lysosomes remain relatively scarce. This review aims to provide a summary of current understanding on the behaviour of lysosomes during autophagy and outline unexplored areas of autophagy-specific lysosome research.

Keywords: Autophagy Lysosomes.

Conflict of interest statement

Conflict of interestThe authors declare that they have no conflict of interest.

Figures

Fig. 1. Autophagy processes.

Fig. 1. Autophagy processes.

Fig. 2. Mechanisms of autophagy machinery recruitment…

Fig. 2. Mechanisms of autophagy machinery recruitment to damaged lysosomes.


BIBLIOGRAPHY

  • Crandall-Stotler, Barbara. "Morphogenetic designs and a theory of bryophyte origins and divergence." BioScience 30(1980): 580-585.
  • Hébant, Charles. The Conducting Tissues of Bryophytes. Vaduz: J. Cramer, 1977.
  • Kenrick, Paul, and Peter R. Crane. The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press, 1997.
  • Miller, Norton G. "Bogs, bales and BTUs: a primer on peat." Horticulture 59 (1981): 38-45.
  • Schofield, W. B. Introduction to Bryology. New York: Macmillan, 1985.
  • Shaw, Jonathon A., and Bernard Goffinet, eds. The Biology of Bryophytes. Cambridge, England: Cambridge University Press, 2000

Distinguishing Characters of Mosses (Phylum Bryophyta), Liverworts (Phylum Marchantiophyta) and Hornworts
(Phylum Anthocerotophyta)


Stranded: How America's Failing Public Transportation Increases Inequality

The nation&rsquos crumbling infrastructure makes it hard for those living in poverty to access jobs, quality groceries, and good schools.

Transportation is about more than just moving people from point A to point B. It’s also a system that can either limit or expand the opportunities available to people based on where they live. In many cities, the areas with the shoddiest access to public transit are the most impoverished—and the lack of investment leaves many Americans without easy access to jobs, goods, and services.

To be certain, the aging and inadequate transportation infrastructure is an issue for Americans up and down the economic ladder. Throughout the country highways are crumbling, bridges are in need of repair, and railways remain inadequate. Improvement to public transportation—buses, trains, and safer routes for bicycles—is something that just about everyone who lives in a major metropolitan area has on their wish list. But there’s a difference between preference and necessity: “Public transportation is desired by many but is even more important for lower-income people who can't afford cars,” says Rosabeth Moss Kanter, a professor at Harvard University and author of a new book Move: Putting America’s Infrastructure Back in the Lead.

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“Without really good public transportation, it's very difficult to deal with inequality,” Kanter said. Access to just about everything associated with upward mobility and economic progress—jobs, quality food, and goods (at reasonable prices), healthcare, and schooling— relies on the ability to get around in an efficient way, and for an affordable price. A recent study from Harvard found that geographic mobility was indeed linked to economic mobility, and a 2014 study from NYU found a link between poor public-transit access and higher rates of unemployment and decreased income in New York City.

Access to good transit is not merely a question of a system’s geographic reach but also the cost to ride—and the latter is becoming an issue more and more. In the past five years many metro areas including New York, Portland, and St. Louis have seen fare hikes that place additional strain on low-income households. Recent additions to public transportation options, like bike share, should—in theory—make getting around easier and cheaper. But as it’s widely been noted, these programs tend to place their kiosks, at least at first, in more affluent neighborhoods. They also require credit cards for rental, which leaves out poorer populations who tend to not have access to such financial instruments. A recent survey of bike share users in Washington D.C., for example, found that ridership wasn’t particularly reflective of the city’s population: The city has a population that is about 50 percent black but the study found that bike-share ridership was made of up of mostly young, white males, and more than 50 percent of those using the region’s bike share system had incomes of $100,000 or more.

That leaves most low-income households to rely on older transportation methods—and therein lies the problem.

For those living in less central neighborhoods, buses typically provide a crucial link to main subway lines. That, too, can be problematic. Bus fleets are old and breakdowns are common. Kanter says that in her interviews with public-transit users, complaints about bus systems were widespread. “They reported that bus drivers sometimes didn't complete routes late at night because there were very few passengers and the neighborhoods were considered dangerous. Or bus drivers would sometimes pass people by standing at bus stops.” Bus stops were also in disrepair, providing inadequate shelter from precipitation or severe cold—a problem that is exacerbated by the book’s finding that even in cities that allow for digital tracking, bus arrival and departure times are often erroneous, leaving people to wait for untold periods of time. And thanks to overcrowding and inadequate space for things like grocery bags or bikes, once a bus arrives, passengers often can’t manage to get on.

That means America’s inadequate public transit leaves many Americans hoping to better themselves stuck—both metaphorically and quite literally.

There is no silver bullet. Kanter says that creating rapid bus service could help increase efficiency and could be completed fairly quickly and require fewer funds than, say, laying rails. And as my colleague Alana Semuels wrote in a recent piece, more public-private partnership may be a solution that helps cash-strapped public systems increase their reach. According to Kanter, the problem has to be addressed, and quickly, especially in the face of growing economic disparity. “We need to think about how important forms of transportation are to the economy and quality of life. And we have to reinvest.”


What is a moss?

A moss is a flowerless, spore-producing plant - with the spores produced in small capsules. The introductory WHAT IS A BRYOPHYTE? page noted that bryophytes have a gametophyte stage and a sporophyte stage. The spore capsule, often with a supporting stalk (called a seta), is the sporophyte and this grows from the gametophyte stage.

You will commonly see the statement that a moss gametophyte consists of leaves on stems. That statement is so close to the whole truth that it's no surprise it's so commonly used.

When a moss spore germinates it first develops a protonema. This is a filamentous to sheet-like growth form, often with a strong resemblance to an algal colony or a fern prothallus. In due course one or more stems grow from the protonema and leaves develop on the stems, giving rise to one or more leafy-stemmed plants. In almost all moss species, the protonemata are ephemeral, with the leafy-stemmed plants the persistent and dominant growth form. But there are exceptions. In some species the protonema is persistent and the leafy part is ephemeral. The term gametophore is used for the stems-and-leaves part and the protonema and gametophore together make up the gametophyte. Now, as already noted, in almost all species the protonema is ephemeral and insignificant when compared with the leafy-stemmed growth. So the leafy-stemmed part is the gametophyte in the great majority of species. It now becomes clear why that fact is often generalized to the statement that the gametophyte in all mosses is leafy-stemmed. For more about the early development, see the LIFE CYCLE SECTION. In contrast to the case in mosses, a liverwort protonema is rudimentary.

The aim of this page is simply to describe the features you can see in a moss - in both the gametophyte and sporophyte stages. You will see some, but by no means all, of the variety in moss gametophytes and sporophytes. This page gives an overview of the features found in mosses and there are links to more details on some of the topics.

While the identification of mosses often requires the use of a microscope, you can learn a lot just by using your eyes and a handlens that magnifies 10 times. In the reference button you&rsquoll find some books with colour photographs of Australian mosses. Looking through them will give you a good introduction to moss diversity.

The following references are very useful for more detail about this great diversity, from the macroscopic view to the microscopic level. Much of the following information on this page has come from these books.

Before going on it&rsquos worth noting that you might confuse mosses with leafy liverworts (which also have a leaves-on-stems gametophyte stage). However, once you&rsquove read this page as well as the WHAT IS A LIVERWORT? page, you will have all the information to let you tell the two apart. For convenience, the distinguishing features of all the bryophytes are summarised on the page that lets you answer the question: WHICH BRYOPHYTE IS IT?

Moss gametophytes

While it may be true to say that a moss gametophyte has "stems and leaves", that statement leaves a lot unsaid. There is a lot of complexity and variety in these &rdquostems and leaves" plants.


Ptychomnium aciculare , showing stems

Stems

Moss stems are generally fairly weak and, if free-standing, fairly short. Stem colour varies from green to shades of brown, for example, Ptychomnium aciculare. Stems are often green when young, with chlorophyll in the cells.

The mosses in the families Dawsoniaceae and Polytrichaceae provide striking exceptions to the general rule stated at the beginning of the previous paragraph. Within these families the stems are fairly firm, with the plants being upright and quite robust. In this photo of a Dawsonia you can see the brown stems quite clearly. Polytrichum or Dawsonia plants can be quite tall, with the free-standing stems of some species growing to over 60 centimetres in height. Hence it is not surprising that people often mistake these mosses for herbaceous flowering plants. Though the stems in the Dawsoniaceae and Polytrichaceae are fairly firm, they contain no lignin and are not woody.

Two growth forms - tufty and trailing

There are essentially two growth forms for moss plants. In one the stems are basically erect, with just one upright stem per plant or with the initial erect stem producing some branches, depending on the species , giving the individual plant a tufty or shrubby appearance. In the other growth form the moss will have mostly trailing stems. If the stems cling to the substrate the overall appearance, to the naked eye, will be of a creeping plant but in some species they hang, almost curtain-like, from branches . The trailing mosses are typically highly branched with the branches growing along the substrate - but many such species also produce short, upright branches. Branches develop from surface cells in the originating stem and in most mosses branches are simple, single outgrowths from the originating stems. In Sphagnum you will see branches developing in fascicles. Within such a fascicle, some of the branches will be stout and spreading, while others are slender and drooping.

In species with an upright growth form the stems may be very short (almost non-existent) to quite long - as already noted for some Dawsonia species. If there is only a very rudimentary stem the plant will look like a bunch of leaves growing from just a single point. In genera like Polytrichum and Dawsonia the individual plants are typically just single stems, with branching rare. Amongst the upright mosses there are the so-called "dendroid" mosses, which have a spread of branches atop a vertical stem . The word "dendroid" means "tree-like" and it's easy to see how apt that term is. In some cases, instead of branches in all directions, there'll be a fan-like spread of branches. You'll also see such mosses called "umbrella mosses" - an equally apt descriptive expression.

There are many erect-stemmed species of moss where the plants grow very closely together in mat-like or cushion-like colonies. In such cases it can be hard (or even impossible) to make out the individual plants, unless you carefully tease apart a small section of the mat or cushion to see what it&rsquos composed of. Here&rsquos a photo of a large colony of a silvery-green moss, Bryum argenteum and here&rsquos a closer view of the upper surface of such a moss colony when wet . You can see a somewhat cobblestone-like surface. If you take a very small sample from the colony and look at it side-on you see this . What you see in the final photo is a small number of individual plants, packed together very tightly.


Leptostomum macrocarpum, showing dead material below

In the case of the cushion-like growth, much of the cushion may be composed of dead material (photo right). As the stems grow, the older leaves (lower down on the stem) die, leaving a living green layer atop a mass of brown, dead material. That brown section will be a mix of rhizoids, dead leaves and stems, and other organic matter that may have been trapped by the plants making up the moss-cushion. You can still make out some leaves in that mass of brown. As the stems continue to grow, more and more dead material will accumulate. Such largely-dead cushions are more characteristic of moist areas, where they can grow to a considerable size. It is common to see sizable green cushions, on rock or trees for example, in moist habitats.

Instead of growing in cushions, you can also get simple-stemmed species where the plants grow separately from each other. Then they look like many small, green fingers poking up from the soil.

In a creeping moss there may be short, leafy branches that grow away from the substrate but such branches are simply off-shoots from the creeping stems. There are also moss species that produce long, trailing stems but where (apart from a small attachment area) the stems don&rsquot cling to anything. In such cases you can see a pendulous, curtain-like growth, such as that of Papillaria flavolimbata .

In some species of clinging, trailing-stemmed mosses the short branches that grow away from the substrate may be very easy to see whereas the clinging stems may be hard to see. For example, the upright branches may be so numerous as to hide the trailing stems or perhaps it&rsquos a species with very few leaves on the clinging stems, so making it harder to realize there is stem there. Or it may be that the main stems are growing in bark cracks or are hidden by leaf litter. In all such cases, unless you look carefully, you could easily mistake the separate upright branches of the one, creeping moss plant as numerous individual plants of a tufted species.

In Gigaspermum repens there is a creeping, largely leafless, underground stem that is rarely seen. All that is visible above ground are short, erect leafy branches (1 to 3 millimetres tall). It would be easy to think of each such leafy branch as a separate plant.

Rhizoids

All mosses have rhizoids. These are anchoring structures, superficially root-like, but without the absorptive functions of true roots. Moss rhizoids are always multi-celled and often branched, whereas liverwort rhizoids are mostly single-celled and rarely branched. Rhizoids are present at the protonemal stage. Once stems have developed rhizoids occur at the bases of stems (in the tufty species) or along the stems (in the trailing mosses). While all mosses have rhizoids, some species may be dense with rhizoids while on others the rhizoids are sparse .

Moss rhizoid systems can be extensive. There are examples of soil mosses where the above-ground plant may be only a centimetre or so in height - but where the rhizoid system reaches three or more centimetres into the soil. Rhizoids aren't roots and don't conduct water and nutrients internally, but a mass of rhizoids can conduct water externally by capillary action. In some species the rhizoids are wound together, almost rope-like, and such strands are very effective at moving water by capillary action.

Leaves

In a dry moss plant the leaves are typically folded into or curled around the stems. In such cases the leaves unfold or uncurl when the plant becomes wet. Thus a moss can look quite different in the wet and dry states. However, there are species where, even in a moist plant, the leaves still clasp the stem.

The individual leaves are small, generally from half a millimetre to three millimetres long. They are always attached directly to the stem, never with a short stalk. In most genera the leaves are just one cell thick, making them translucent. In many such genera the leaves are thickened along their long central axes. Such a thickening is called a nerve or costa. There are a few genera (such as Leucobryum and Sphagnum) where the leaves are several cells thick. Moss leaves generally taper to the tip (though the tapering may be sudden or gradual). The tip may continue as a long hair-like extension, called a hairpoint.


Campylopus introflexus, showing hair points

The photo (right) shows a colony of Campylopus introflexus, a common and widespread species in Australia. In this species each leaf has a hairpoint and the photo shows the hairpoints quite clearly. Leaf bases may vary, depending on species, being anything from much narrower to much wider than they are at mid-leaf, and they may be long or short in relation to width. The leaves typically have smooth or almost smooth margins. The margins may be toothed but you don't get the heavily divided leaves that are common in the leafy liverworts.

Different parts of the plant may have different types of leaves. For example, in many trailing species the leaves on the upright branches are different to those on the creeping stems. In many mosses, whether trailing or tufty, the leaves that surround the egg and sperm producing organs differ from the other leaves on the plant.

There's more about bryophyte leaves in the LEAF SECTION.

Antheridia and archegonia

The male and female gametes (eggs and sperm) are produced on the gametophyte (in special structures called antheridia and archegonia, respectively) and a fertilized egg will develop into a sporophyte. Thus the spores are part of the sexual reproduction cycle. There's more about this in the REPRODUCTION SECTION. Mosses can be divided into two broad groups, depending on where the archegonia are produced. In the acrocarpous mosses the archegonia are produced at the ends of the main stems. In the pleurocarpous mosses the archegonia are produced on short side-shoots, not on the main stems.

Moss sporophytes

A moss sporophyte consists of a spore-containing capsule, possibly sitting atop a stalk (called a seta). In this photograph you can see many brownish sporophytes (the stalked spore capsules) that have grown from the greenish, leafy-stemmed gametophyte. The sporophyte's development is discussed in the SPOROPHYTE DEVELOPMENT SECTION.

In almost all moss species the capsule has a well-defined mouth at the end opposite the stalk or the point attaching the capsule to a stem. When there is a mouth, the spores are released through that mouth. There is a very small number of mouth-less mosses - such as species of the genus Andreaea. This genus is commonly found in polar areas and in sub-alpine to alpine areas (and even alpine areas in the tropics). The capsules of Andreaea do not have mouths. Instead they open by slits in the sides of the capsules. In some genera (such as Archidium) the capsules have neither mouths nor splits in their slits in their sides. Instead, the capsules rupture irregularly.

The mature spore capsule may (depending on species) hang down, stick up - or be held at any angle in between. The way the capsule opens (mouth, side slits, irregular rupturing) and the orientation of the capsule play important roles in the way in which spores are released and there's more about spore dispersal in the in DISPERSAL SECTION.


Watch the video: Σύστημα μεταφοράς FoppaPedretti Supertres - ΛΗΤΩ Βρεφικά πολυκαταστήματα (November 2021).