106 PLANTS, THE FOOD OF ANIMALS 



heavy aerial structures, while complicated canal systems for the 

 transportation of salts and foods in solution penetrate the entire 

 plant organism from the tiniest rootlet to the tips of the highest 

 leaves. The reproductive organs, finally, are equally well 

 developed in plants and animals, the maintenance of species 

 being a universal biological need. 



Plants, like animals, are divided into two great groups, proto- 

 phyta and metaphyta, although these designations are not 

 often used in classification. The metaphyta bear the same 

 relation to the protophyta that the metazoa bear to the pro- 

 tozoa, viz., many-celled as contrasted with single-celled organ- 

 isms. For our purposes a glance at each type will suffice to 

 give a clear understanding of the essential relationships of 

 animals and plants, and show that, except for the functions of 

 nutrition, the fundamental biological principles in animals 

 and plants are the same. 



B. PLEUROCOCCUS PLUVIATILIS AND SPHAERELLA LACUSTRIS 



These two organisms are good types of the unicellular plants, 

 the former existing as quiescent non-motile cells, the latter 

 having two phases, one motile, the other not. As unicellular 

 forms they are allied to a large number of low types of plants 

 included in the group known as Algae, in which some forms 

 are included which cannot be accurately determined as plants 

 or as animals. Some of these, like the Peridiniales or Dino- 

 flagellata and the Volvocidae, are included by botanists as 

 plants, by zoologists as animals. 



Pleurococcus is widely distributed in damp places, where 

 it exists as a green covering to stones, tree trunks, ground, etc. 

 Each cell is composed of protoplasm differentiated into cyto- 

 plasm and nucleus, and contains minute grains of starch. 

 Green coloring matter, chlorophyll, is uniformly distributed 

 throughout the cell, which, finally, is covered by a transparent 

 coating of cellulose, a characteristic plant product similar in 

 chemical composition to starch but with a different arrange- 

 ment of molecules. Reproduction occurs by simple division, 

 the daughter cells separating when formed, or remaining to- 



