ALG& CONTINUED: CLASSIFICATION. 



'59 



ponds, ofcere in dry weather it is often found closely adhering to the dry 

 rock surface, and giving it a reddish color as if the rock were painted. T his 

 is especially the case in the shallow basins formed over the uneven surface 

 of the rock near the water's edge. These places during heavy rains or in 

 high water are provided with sufficient water to fill the basins. During 

 such times the red snow plant grows and multiplies, loses its red color and 



c 



Fig. 163. 



Sphaerella lacustris (Girod.) Wittrock. A, mature free-swimming individual 

 with central! red spot. B, division of mother individual to form two. C, divi- 

 sion of a red one to form four. D, division into eight. E, a. typical resting cell, 

 red. F, same beginning to divide. G, one of four daughter zoospores after 

 swimming around for a time losing its red color and becoming green. (After 

 Hazen.) 



becomes green, and, being motile, is free swimming. It is a single-celled 

 plant, oval in form, surrounded by a gelatinous sheath and with two cilia 

 or flagella at the smaller end, by the vibration of which it moves (fig. 162). 

 The single cell multiplies by dividing into two cells. When the water dries 

 out of the basin, the motile plant comes to rest, and many of the cells assume 

 the red color. To obtain the plant for study, scrape some of the red cov- 

 ering from these rock basins and place it in fresh spring water, and in a da] 

 or so the swarmers are likely to be found. Under certain conditions small 

 microzoids are formed. 



336. Chlamydomonas is a very interesting genus of motile one-celled 

 green alg, because the species are closely related to the Flagellates among 

 the lower animals. The plant is oval, with a single chloroplast and sur- 

 rounded by a gelatinous envelope through which the two cilia or flagella 

 extend. One-celled organisms of this kind are sometimes called monads, 

 i.e., a one-celled being. This one has a gelatinous cloak and is, therefore, 

 a cloaked monad (Chlamydomonas). The species often are found as a very 

 thin green film on fresh water. C. pulvisculus is shown in fig. 163. When 

 it multiplies the single cell divides into two, as shown in B. Sometimes a 

 non-motile palmella stage is formed, as shown in C and D. Reproduction 



