116 BOTANY. 



239. Nearly all the plants of this group contain chloro- 

 phyll, only one order being destitute of it. The green 

 forms are all aquatic, and inhabit either fresh or salt water. 

 Those which have no chlorophyll are mostly saprophytes, 

 and live upon dead organic matter. They are doubtless to 

 be regarded as modified forms of some of the types of the 

 chlorophyll-bearing portion of the group. 



240. Two classes of Unisexual plants have been distin- 

 guished, as follows: 



1. Sexual cells locomotive — Zoospores. 



2. Sexual cells fixed — Comjugatm. 



CliASS I. ZoOSPOEB^. 



241. In this large class the protoplasm is quite in the 

 habit of escaping from the plant and taking on a locomo- 

 tive state, in which it is called a zoospore, a word which 

 means an animal-like spore (from the Greek soon, an ani- 

 mal). Under the microscope a zoospore looks very much 

 like a monad, and this resemblance is made still greater 

 when we observe the cilia by which it darts rapidly through 

 the water. All the plants of this class contain chlorophyll. 



242. Fandorina is the pretty name given to a fresh-water 

 plant of this class. It consists of a globular colony of green 

 cells, each cell provided with two cilia, which project out- 

 ward from the ball, and by rapid vibration give it a rotary 

 motion (Fig. 50). At a certain stage of its development 

 some of the cells of the colony escape and swim about in 

 the water; finally two come in contact with one another 

 and unite, forming a resting spore {E, F, G, H, Fig. 60). 

 After a period of rest, the resting spore bursts its wall, the 

 protoplasm escapes, swims about for a time by means of 

 two cilia with which it is provided; at last it comes to rest 



