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—Zodsporea. 
2. Sexual cells fixed—Conjugata. 
Crass I, ZoédsporEs. 
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 zodspore, a word which 
means an animal-like spore (from the Greek zoén, an ani- 
mal). Under the microscope a zodspore 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, Pandorina 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). Ata 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 (Z, ¥, G, H, Fig. 50). 
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 
