222 



GENERAL MORPHOLOGY OF PLANTS 



in small, oval, flattened chloroplasts. They multiply by the for- 

 mation of special bodies from the protoplasm of individual cells. 

 These bodies are called spores, and are provided with cilia so 

 that they swim about in the water after escaping from the parent 

 cell. They are thus called " swimming spores" " zoospores " 

 or " zoogonidia" These spores are not formed as the result 

 of a sexual process. The process is an asexual one, hence 

 they are often termed asexual swimming spores. Sexual repro- 

 duction takes place in some by the fusion of two swimming 

 spores, similar to the asexual spores, forming a zygospore. In 

 others definite sexual organs are formed, a large one, the female 

 organ, an egg case (called an oogonium), which contains the egg or 

 ob'spore; and a smaller one, the male organ, a sperm case (called an 

 anlheridium), containing a number of small motile male cells, the 

 sperms. Fertilization in these results from a fusion of a sperm with 

 the nucleus of the egg. 



364. Ulothrix. Ulothrix is an example of the first kind of 

 sexual reproduction described above. The plant forms simple 



threads. In asexual re- 

 production a number of 

 small, oval, 4-ciliated swim- 

 ming spores are formed 

 from the protoplasm of a 

 single cell. These escape, 

 and after the swimming 

 period come to rest, ger- 

 minate and produce the 

 Ulothrix thread again. In 

 sexual reproduction similar 

 biciliate swimming spores 

 are formed which unite in 

 pairs to form zygospores 

 (fig. 176). Cladophora, 

 Chcetophora, Drapernau- 

 with a similar method of 



c 



Fig. 176. 



Ulothrix zonata. A, base of thread. B, cells with 

 zoospores, C, one cell with zoospores escaping another 

 cell with small biciliate gametes escaping and some 

 fusing to form zygospores; E, zoospores germinating 

 and forming threads; F, G, zygosoore growing and 

 forming zoospores. (After Caldwell and Dodel.) 



dia, etc., are 

 reproduction. 



branched forms 



