182 cnrproGAMs 



tricliogyne ; the}' surruiuid themselves by membranes, and 

 the euuteuts of one of them pusses through the trichogyne 

 Avail and makes its way to the egg uell. After fertilization 

 the fertilized egg (oospore), remaining in position, divides 

 and, on all sides, sends out branches (Fig. 300, c), from 

 which separable cells, called carpospores, are finally formed. 

 These spores serve the same purpose as the tetraspores, 

 growing directly to new plants. 



436. It is to be noted that wliile in Vauoheiia and Rockweed the 

 oospore is set free fi-om the parent plant before germiuation and 

 grows directlj' to a new plant, iu jSTemalion the corresponding body 

 (fused egg cell and pollinoid) Is not liberated fiom the carpogonium, 

 but, as we may say, gernnnates in position. The free spores are pro- 

 duced only iifler an interval of growth. 



437. ^\'e summarize reproduction in the types of Green, Brown, 

 and Red Alg;c as they have here been described, as follows : — 



(1) Fveproductive cells give rise to new jdants iclthoul coiijiirjatinr/. 

 A single cell, set free from the parent, gerjuinates without having to 

 fuse with another cell. This single cell is a spore: in Ulothrix and 

 Brown Algfe, a zoospore; in Red Alga;, a tetraspore or a carpo- 

 spore. 



(2) Reproductive cells conjugate before giving rise to new plants. 

 Two cells unite to make up a Ijody which is the starting point of 

 a new plant. The uniting cells are gametes. Gametes may be : 

 (a) zoospores (zoogainetes), indistinguishable in some cases from the 

 zoospores which germinate without conjugating; (6) pairs of similar 

 unciliated cells (Spirogyra); (c) egg cells and antherozoids or polli- 

 noids (Vaucheria, Rockweed, Nemalion). The egg cell may be 

 fertilized in position (Vaucheria, Nemalion), or after lilieration (Rock- 

 weed). The immediate result of conjngatioii is a zijgospore when the 

 uniting cells are alike ; an oospore, when they are unlike. The oospore 

 may be freed fi'ovn tlie oogonium before it germinates (Vaucheria, 

 Rock«ei-'d). in which case flie reproduction is described as oos/iorlc ; 

 or may df'vflop in position (Xemalion), cai'pospores being the indirect 

 result, in whicli case the repi-oduclii.m is said to be car/jcis/mric. In 

 Vaucheria and RoekwHed the germination of I lie oospore gives a new 

 plant; we may propei'ly, therefore, think of the structure resulting 

 from the fertilization of the egg in Nemalion (namely, the branches 

 of the carpogonium and the carpospores while forming) as a new 

 plant parasitic upon the parent. 



(o) Reproduction viihoul cnnjugation serves for rapid propagation ; 

 and at tlie same time for dispersion, since the spores are often motile, 

 and when unciliated float easily in the water. 



