37 o BOTANY OF THE LIVING PLANT 



is commonly present in Green Algae. The general physiology of a 

 coenocytic, or, as it has been called, a non-cellular plant, is probably 

 like that of any ordinary green plant. The difference lies in the 

 mechanical construction. 



Vegetative propagation is carried out in various Siphonaceous 

 Algae by non-motile, or by motile cells, produced in large numbers 

 in "special branches, and liberated into the water. Vaucheria is an 

 exception, in that the whole contents of such a branch-ending, which 

 are previously shut off by a septum, are discharged as a single ciliated 

 zoospore, large enough to be seen with the naked eye. The escape 



Ftg. 275. 

 Gametes of various Siphonales, illustrating differentiation of male and female. 

 i=Acetabularia, isogametes ; ii = Bryopsis ; iii=Codium; iv =Vaucheria. In ii 

 and iii the gametes are unequal, but still motile ; iv in the large egg is stationary, 

 while the smaller spermatozoid is motile. (Taken from Oltmann's Algae.) 



is effected in the early morning ; after a period of movement the 

 zoospore comes to rest, and germinates directly into a new plant 

 (Fig. 274). In structure the zoospore shows the cilia in pairs, each 

 pair related to a nucleus which is superficial, while the chloroplasts 

 lie within. The origin and structure of the zoospore suggests that 

 it represents the undivided contents of a whole zoosporangium, such 

 as may be seen in other Siphonales. 



The Siphonales reproduce sexually : but degrees of difference in 

 size of the gametes are seen. The differentiation thus indicated must 

 be held as distinct from, though parallel with that already described 

 in the Volvocales and in the Ulotrichales and Oedogoniales. In 

 Acetabularia the gametes are of equal size, and those produced from 

 different gametangia, or from different plants fuse in pairs (Fig. 275, i.). 



