I 



CHAPTER 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 ^^hich 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 r.r 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 difterentiation 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, ordiiuirily formed 

 by cell division, is followed by the appearance of the sexual 

 spore, formed by cell union, the act of cell union being 

 knov/n 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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