Chapter 11. Bryology ~ The Liverworts and Mosses
Bryology is the study of nonvascular complex plants classified in the Division Bryophyta.
The Bryophytes have several adaptations that allow them to grow on land, but are still tied to moisture for their reproduction. Their size is also restricted because they do not have vascular tissues, which limits their height and keeps them close to the nutrition and moisture of the ground. Rhizoids anchor them to the ground, but do not conduct water or nutrients as roots do. Some mosses have developed pores, but they do not open and close as stomata do.
Most mosses look like undifferentiated green mold on rocks, but while they are non vascular, they have complex forms and parts. They have what appear to be leaves coming off their stalks, but are not leaves because they have no veins. Most notable in their anatomy is the peculiarity of their life cycle. The haploid organism is actually most of what we would call the moss. That green mat is the gameteophyte contains half of the DNA, or one full set of chromosomes. When the female gametophyte is fertilized with motile sperm from the male gametophyte, the diploid sporophyte grows directly out of the gametophyte. So out of an ordinary spiky green moss stalk, a tall curved stalk grows, with a large cap on it. That structure is the sporophyte. It will produce spores (that are haploid) that will propagate more haploid mosses. Each successive evolutionary adaptation of plants has reduced the haploid stage in size, and increased the diploid, or sporophyte stage. In ferns, the next evolutionary innovation based in bryophytes, the gametophyte stage functions the same way as here, the haploid spores make a haploid organism, which after fertilization grows a full diploid sporophyte from it. However, what we know as a fern is the diploid organism, the gametophyte is a very small heart shaped organism at the base of the fern. Read:
11.1 Out of the mosses, the liverworts and the hornworts, do any of these have seeds? 11.2 How are bryophytes similar to the algae? How are they different? 11.3 How is a spore different from a seed? How many sets of chromosomes does a spore have (1N or 2N)?
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