NOTE LICHENS AND MOSSES ARE COMPLETELY UNRELATED TAXONOMICALLY BUT ARE
SIMPLY COVERED IN THE SAME LAB.
THERE ARE FOUR LIFE FORMS OF LICHENS
Lichens - growth from that is appressed, "crusty" in appearance, and
in direct contact with substrate (ex. flattened, crusty lichen on a tree
branch). Has organization of the above but with an lower cortex and
scattered algal cells.
Foliose Lichens - similar to crustose lichens in cross-section but leafy in appearance.
Fig. 2 Crustose / Foliose lichen cross-section.
From left to right, upper cortex, scattered algal cells, medulla, and finally lower cortex.
Lichens -highly branched structure with a thick outer cortex, medulla
and distinct algal layers.
Fig. 1 Fruticose Lichen Cross Section showing cortex, medulla, algal cells.
Gelatinous Lichens - different
from the above three lichens in that is is made mostly of blue-green algae
(Cyanophyta) with only a little fungus present. The gelatinous appearance
is from the mucilage commonly found on the exterior of blue-green algae
Bryophytes can be defined as green plants that lack well developed vascular tissues (such as a xylem and phloem). They have motile sperm, chlorophylls a and b, and generally are very slow growing. Because they don't have well developed vascular tissues, they cannot conduct water and nutrients the way a vascular plant would. This forces their growth form to be low to the ground so they can absorb water and minerals through capillary action. They are not considered to have true leaves or roots even though they may have structures that appear leafy. Even though they may be referred to as "leaves" they are much simpler than leaves seen in plants thus far. They often use rhizoids as an anchor to the substrate. These rhizoids do not conduct water or nutrients but instead allow the plant to stay attached to its surface while absorbing water and minerals through capillary action. They also have sporophytes which are spore producing structures. The sporophyte results from fusion of the egg formed in the archegonium) and the flagellated, motile sperm formed in an antheridium.
The bryophyte seen in lab this week are the MOSSES. Early in the semester we did see another group of Bryophytes the LIVERWORTS. There is a third group called the HORNWORTS which will not be covered this semester.
MOSSES: Handout provided in class goes into a detailed description of the reproductive cycle. Listed below is a similar description with some pictures listed on web page
Mosses are able to reproduce similarly to higher, flowering plants. Plants in the gametophyte stage are able to re-produce sexually, in a similar way to flowering plants. However, the reproductive parts are small and not showy like flowers. There are two stages, the gametophytic and the sporophytic. First meiospores germinate into a protonema. The protonema develops into the leafy gametophyte that we commonly see. From there male, female or both structures are produced either at the growing tip or laterally to the plant branches (see Acrocarpous and Pleurocarpus below). The male organs are known as antheridia. The antheridium encloses the sperm which are released when the antheridial wall ruptures. The sperm use a film of water to swim toward the egg. The female organs are known as (archegonia). The archegonia is surrounded by neck and ventral canal cells. These break to allow the sperm passage to the egg. After fertilization occurs, a new plant develops, which is attached to the parent plant. This is the sporophyte.
The sporophyte is made of a
which is on the end of a thin stalk (seta) (click
here for capsule and seta picture). The capsule has a covering
known as an operculum.
There may also be tiny teeth present underneath the operculum called the
teeth. The mature capsule contains large numbers of microscopic
spores called meiospores. These are eventually released and dispersed
(usually by wind) and each is then capable of germinating to eventually
develop into a new gametophyte plant.
THERE ARE THREE LIFE FORMS
Sphagnum Mosses - spirally arranged "leaves" and very branched and clustered. Sphagnum mosses form their sporophytes like the acrocarpous mosses and have been observed to forcibly fire their spores up to 2 meters.
Acrocarpous Mosses - distinguished by the sporophyte being very erect, (i.e. extending up and away from the main plant body). Since sporophytes are so often present this moss can usually be distinguished by erect structures. This structure forms because the apical (growing tip) is where to sporophyte forms so it is out on the end of a branch or leaf.
Pleurocarpus Mosses - distinguished by the sporophyte being low to the ground. May be harder to identify in the absence of sporophytes but mosses generally hugs the ground more so than acrocarpous mosses. The sporophyte does not form on the growing tip but instead on a side (lateral) branch.
to Internet Resources for Bryologists and Lichenologists
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