182 CRYPTOGAMS 



tricliogyne ; they surround themselves by membranes, and 

 the contents of one of them passes through the trichogyne 

 wall and makes its way to the egg cell. 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 caiyospores^ are finally formed. 

 These spores serve the same purpose as the tetraspores, 

 growing directly to new plants. 



436. It is to be noted that while in Vaucheria and Rockweed the 

 oospore is set free from the parent plant before germination and 

 grows directly to a new plant, in IS^emalion the corresponding body 

 (fused Qgg cell and poUinoid) is not liberated from the carpogonimn, 

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

 duced only after an interval of growth. 



437. We summarize reproduction in the types of Green, Brown, 

 and Red Algae as they have here been described, as foUow^s : — 



(1) Reproductive cells give rise to new plants ivitliout conjugating. 

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

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

 Brown Algse, a zoospore ; in Red Algae, a tetraspore or a carpo- 

 spore. 



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

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

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

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

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

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

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

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

 weed). The immediate result of conjugation is a zygospore w^hen the 

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

 may be freed from the oogonium before it germinates (Vaucheria, 

 Rockweed), in which case the reproduction is described as oosporic ; 

 or may develop in position (Nemalion), carpospores being the indirect 

 result, in which case the reproduction is said to be carposporic. In 

 A^aucheria and Rockweed the germination of the oospore gives a new 

 plant; we may properly, 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. 



(3) Reproduction loitJiout conjugation serves for rapid propagation ; 

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

 and when unciliated float easily in the water. 



