i86 ADVANCED FORMS OF REPRODUCTION 



repeatedly notice variations of this nature. In the development 

 of plants advances are often confined to one or another feature 

 of their organism which may become highly developed and spe- 

 cialized ; at the same time one or more features may be retained 

 that have been subject to little or no variation and which, there- 

 fore, remain in a primitive state. 



Fig. 115. Growth and asexual reproduction of Oedogonium: A, young 

 plant showing basal cell modified as a hold-fast. B, two cells of a filament, 

 in one of which a zoospore is forming and the other cell has opened, per- 

 mitting the escape of the zoospore shown at C. D, zoospore at rest. It 

 becomes attached to an object at its colorless, ciliated end. E, later stage 

 in the germination of the zoospore. — After West. 



71. Other Members of the Green Algae. — ^There are several 

 orders of the Chlorophyceae, some of which are marine, that 

 cannot be considered at this time. Two genera, however, de- 

 serve attention because they show significant advances in the 

 evolution of plant life. In Oedogoniiim, a member of a small 

 order, the Oedogoniales, we find a still higher form of the sexual 

 reproductive process. These plants are of very common occur- 

 rence in ditches, streams and springs where their filaments form 

 for a time greenish masses and coatings upon various objects, 

 but finally become detached and free-floating (Fig. 115, A). 

 Any of the cells of a filament, save the basal one, may form a 

 single zoospore, which are large pear-shaped bodies with a narrow 

 colorless end around the base of which arise a circle of numerous 



