•238 



PLANT STUDIES 



is the low type called isogamy, the pairing gametes being 

 alike. 



Ulothrix is taken as a representative of the Conferva 

 forms, the most characteristic group of Chlorophycese. All 



3?IG. 205. Ulothrix, a Conferva form. A, base of filament, showing lowest holdfast 

 cell and five vegetative cells, each with its single conspicuous cylindrical chloro- 

 plast (seen in section) inclosing a nucleus ; B, four cells containing numerous 

 email zoospores, the others emptied; C, fragment of a filament showing one cell 

 (a) containing four zoospores, another zoospore (b) displaying four cilia at its 

 pointed end and just having escaped from its cell, another cell (c) from which 

 most of the small biciliate gametes have escaped, gametes pairing (d), and the 

 resulting zygotes (e) ; D, beginning of new filament from zoospore; E, feeble 

 filaments formed by the small zoospores ; F, zygote growing after rest ; G, 

 zoospores produced by zygote. — Caldwell, except F and Q, which are after 

 Dodel-Port. 



the Conferva forms, however, are not isogamous, as will be 

 illustrated by the next example. 



165. (Edogonium. — This is a very common green alga, 

 found in fresh waters (Fig. 206). The filaments are long and 

 simple, the lowest cell acting as a holdfast, as in Ulothrix 



