340 



THE SIMPLEST PLANTS 



single cells or clusters of cells, the cells of spirogyra are 

 cylindrical in shape and are attached end to end. This 

 results in long, fine threads which float in the water in 



large masses. 



The individual cells of spirogyra are provided with one 

 or more narrow green bands arranged spirally within the 



t" — r"" 1 -?^ |fT ;-;T)^^» J • <v ^ :v ■■ ."-■■ ^ 





v^~ 



<hJ 





Figure 364, — Spirogyra. 



protoplasm. These spiral bands of chlorophyll are the 

 special structures which manufacture food (Figure 364). 

 The cells of the filament increase rapidly in size and di- 

 vide, and thus the filaments increase in length. As each 

 cell divides, the cell wall grows in at right angles to the 

 length of the plant. Spirogyra grows so rapidly in the 



spring that in a short 

 time the water may be- 

 come polluted. The 

 bubbles found among a 

 mass of spirogyra are 

 the oxygen which the 

 cells give off during 

 photosynthesis. 



During the summer 

 there are times when spirogyra reproduces in another 

 manner (Figures 365 and 366). Two cells of adjacent 

 plants join by putting forth tubes which fuse on meeting. 

 The contents of one cell pass through the tube, and flow 

 into and unite with the contents of the other cell. Thus 

 there is formed a single roundish mass of protoplasm 

 surrounded by a thick wall. This mass of protoplasm 



Figure 365. — Spirogyra Conjugating. 



