340 



FOUNDATIONS OF BOTANY 



409. Messmates.^ — Plants of very diverse character^ 

 which live most intimately together to the advantage of 

 both parties, may be called messmates, since in some fashion 



or other they divide the 

 food supply between 

 them. 



Bacteria live in col- 

 ionies enclosed in root- 

 tubercles on the roots of 

 certain plants, for in- 

 stance, beans, peas, lu- 

 j pines, vetches, and clover 

 (Fig. 236), and render 

 the greatest service to 

 the plant to which the 

 roots belong, from which 

 they also derive food and 

 shelter. Such plants do 

 not develop root- 

 tubercles and will not 

 grow well in sterilized 

 soil, that is, soil in which 

 the bacteria have .been 

 killed by baking. It is 

 found that the bacteria 

 serve to change nitrogen 

 taken from the air of the soil into nitric acid, which is a 

 most important ingredient in the manufacture of prdteids. 

 Many trees, for example, oaks, beeches, and the cone- 



1 This term is borrowed from the zoologists as a much simpler one than 

 gymbionts to express the relation variously known as symbiosis, commensalism, 

 or mutuaMsm. ^ Sarracenia purpurea. 



Fig. 237. — Common Pitcher-Plant.^ 



At the right one of the pitcher-like leaves is 

 shown in cross-section. 



