28 PLANT LIFE 



renders possible the production of those 

 almost infinitely complex substances which 

 form the very substratum of life itself. 



CHAPTER III 



EVOLUTION OF CELLULAR STRUCTURE IN 

 SIMPLE PLANTS 



EMPHASIS has already been laid on the 

 circumstance that the plant cell, owing to 

 the presence of its investing skin of cellulose, 

 is only able to absorb and use substances 

 capable of diffusing through the membrane. 

 Consequently food from without can only 

 reach the protoplasm in solution. Salts 

 and other solid food materials are invariably 

 absorbed in a state of solution, and the same 

 is true of gases, such as oxygen and carbon 

 dioxide, as well. 



But water has other functions to discharge 

 within the plant, besides that of serving as a 

 vehicle for the intake of nutritive materials. 

 It serves to maintain the protoplasm itself 

 in that characteristic semi-fluid condition 



