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. no. 



FIG. in. 



FIG. no. 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. in. 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- 



