36 MORPHOLOGY 



after the partition wall is formed, it becomes uninucleate by the 

 degeneration of the other nuclei. In the wall of the oogonium a more 

 or less beaked opening is formed by which the sperms enter. The 

 antheridial branch is similar in origin, but is longer, the antheridium 

 being cut off at the curved tip by a wall as a small cell. In other 

 species a single sexual branch bears both oogonia and antheridia 

 (fig. 98), a common arrangement of the cluster being a terminal 

 antheridium and a group of laterally developed oogonia. In each 



FIGS. 98-100. Vaucheria: 98, 99, two methods of forming oogonia and antheridia; 

 in both cases the terminal antheridium has discharged its sperms (100). 100, after 



WORONIN. 



antheridium numerous sperms are formed (fig. 100), which are dis- 

 charged, enter through the beaked openings of the oogonia, and 

 fertilize the eggs. The heavy-walled oospore is the protected stage 

 of the plant and germinates directly into a new filament. 



Experiments. The experiments upon Vaucheria are of great interest, since by 

 varying the character of the medium, the nature of the nutrition, the light, etc., 

 there may be produced at will sterile plants, zoospore-producing plants, or gamete- 

 producing plants. Vaucheria also has great power of resisting unfavorable condi- 

 tions, in the presence of which the filament becomes chambered by the formation 

 of thick cross walls, and the contents of each compartment round up as an aplano- 

 spore. In favorable conditions each aplanospore either forms a new filament 

 directly, or discharges an amoeba-like protoplast, which rounds off as a green sphere, 

 covers itself with a wall, and either forms a filament directly or enters again into 

 a period of rest. This ability to respond promptly to varying conditions and 

 to change the program at almost any period in the life history is very marked 

 among the lower plants. 



