DEVELOPMENT OF PLANTS 



171 



zoospores through an opening formed in the cell • wall (Fig. 

 in, A). The cells in which the zoospores are formed are called 

 sporangia. The zoospores resemble the motile plants noted 

 above, but after a short motile period they return to the stationary 

 condition and grow into new plants (Fig. in, C). In this way, 



Fig. i 10. 



Fig. hi. 



Fig. 1 10. Lower portion of Ulothrix, the basal cells are somewhat 

 modified and the lowest one acts as an anchoring organ. Each of the 

 upper cells contains a girdle-like chloroplast. 



Fig. ill. Asexual reproduction of Ulothrix: A, a few cells of a fila- 

 ment in the upper cells of which the formation and escape of the large 

 zoospores are shown, while in the lowest cells a large number of small 

 zoospores appear. B, a large zoospore. C, a young plant formed from B. 

 D, a small zoospore. E, a young plant formed from D. — After West. 



the number of plants is rapidly multiplied and it should be stated 

 that the asexual method of reproduction may be looked upon as 

 •a means of bringing about a rapid increase in the number of indi- 

 viduals of a species while the conditions for growth are favor- 



