CHAPTER VIII. 



BRANCH II. PHYCOPHYTA. 



THE SPOKE-TANGLES. 



229. This is an assemblage of quite diverse plants, rang- 

 ing from minute unicellular species, on the one hand, to 

 large seaweeds of considerable complexity, on the other. 



230. In this branch we find the first examples of un- 

 doubted sexuality, that is, the production of new plants as 

 a result of the union of two masses of protoplasm. In the 

 simpler cases there is no appreciable difference as to form, 

 size, color, origin, etc., between the uniting cells {gametes), 

 but in the higher ones the gametes differ greatly. The 

 immediate result of the union of the two sexual cells is the 

 production of a new cell, the resting spore, zygospore, or 

 oospore, possessing very diif erent characteristics from either. 

 While the sexual cells have only ordinary walls, or none at 

 all, the resting spores are covered with thick, firm walls. 



231. The resting spore is so called because under certain 

 circumstances it remains quiescent, while retaining its vi- 

 tality, often for long periods of time. Thus at the close 

 of the growing season, as upon the advent of the summer 

 drought, or of winter, the resting spores fall to the bottom 

 of the pools (in the fresh-water forms), and in the dried or 

 frozen mud remain uninjured until the return of favorable 

 conditions, when they germinate and give rise to a new 

 generation of plants. 



232. iJfearly all the plants of this group cont^-in chloro- 



183 



