CHAPTEE XIX 
BRYOPHYTES (MOSS PLANTS) 
195. Summary from Thallophytes. Before considering the 
second great division of plants it is well to recall the most 
important facts connected with the Thallophytes, those 
things which may be regarded as the contribution of the 
Thallophytes to the evolution of the plant kingdom, and 
which are in the background when one enters the region of 
the Bryophytes. 
(1) Increasing complexity of the ~body. Beginning with 
single isolated cells, the plant body attains considerable 
complexity, in the form of simple or branching filaments, 
cell-plates, and cell-masses. 
(2) Appearance of spores. The setting apart of repro- 
ductive cells, known as spores, as distinct from nutritive 
cells, and of reproductive organs to organize these spores, 
represents the first important differentiation of the plant 
body into nutritive and reproductive regions. 
(3) Differentiation of spores. After the introduction of 
spores they become different in their mode of origin, but 
not in their power. The asexual spore, ordinarily formed 
by cell division, is followed by the appearance of the sexual 
spore, formed by cell union, the act of cell union being 
known as the sexual process. 
(4) Differentiation of gametes. At the first appearance 
of sex the sexual cells or gametes are alike, but after- 
ward they become different in size and activity, the large 
passive one being called the egg, the small active one the 
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