20 



PLANT MORPHOLOGY 



a large central vacuole. Such a multinucleate body, without any cross 

 walls, is called a coenocyte. Food is stored as oil or leucosin. 



Asexual reproduction may occur either by zoospores or aplanospores. 

 When covered with water, the entire aerial portion may release numerous 

 uninucleate zoospores through a terminal pore. The zoospores have two 



D 



Fig. 9. Tribonema homhycinum, a yellow-green 

 alga. A, portion of vegetative filament; B, aplan- 

 ospores; C, zoospores; D, structure of cell wall, as 

 revealed by special treatment. {A, B, C, after Gay; 

 D, after Bohlin.) 



Fig. 10. Botrydium 

 granulatum, showing 

 balloon-shaped aerial 

 portion and branched 

 subterranean portion, 

 X20. 



cilia of unequal length, attached anteriorly. They may either germinate 

 immediately or form a wall and go into a resting stage. In the absence 

 of sufficient moisture, the aerial portion may give rise to aplanospores or 

 all the cytoplasm may move into the rhizoidal portion and there produce 

 aplanospores. The aplanospores of Botrydium may be either uninucleate 

 or multinucleate and, after a dormant period, may give rise either to zoo- 

 spores or to new plants directly. Sexual reproduction is accomplished 

 by small biciliate isogametes, each with a single nucleus, that fuse to 



