The Algae 



445 



is also used as an absorbent of nitro-glycerine in making dyna- 

 mite, and in the manufacture of fireproof linings and walls. 



Fig. 274. Chlamydomonas, a simple free-swimming form of green alga. 

 Four stages in the reproduction of the plant are shown above. {After Dill.) 



THE GREEN ALG^ OR CHLOROPHYCE^ 



Probably no other group of plants exhibits as wide a range of 

 forms, structures, and life histories as the green algae. So great 

 is this diversity that it is exceedingly difficult to describe the 

 group as a whole. More than 5000 species have been described, 

 and these are scattered among many families, the interrelation- 

 ships of which are far from clear. 



The green algae include unicellular forms, simple and branched 

 filaments, plates or extensive sheets, and small gelatinous masses. 

 All possess chlorophyll inclosed in definite chloroplasts, which 

 also have an almost endless variety of form. The cell walls are 

 variously formed of cellulose and pectic compounds. Some of 

 the forms have an outer layer of chitin on the wall. Most of the 

 green algae produce motile cells at some stage in their develop- 

 ment. In the simplest forms the motile stage is the most promi- 

 nent one in the life history. 



The green algae are of peculiar interest, because among them 

 are not only the simplest plants containing a definite nucleus 

 and chlorophyll-bearing structure in the protoplasm, but also 

 the types of plants from which the more complex land plants are 



