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 
Fia, 237. — Common Pitcher-Plant.? 
At the right one of the pitcher-like leaves is 
shown in cross-section. 
or other they divide the 
food supply between 
them. 
Bacteria live in col- 
onies enclosed in root- 
tubercles on the roots of 
certain plants, for in- 
stance, beans, peas, lu- 
pines, vetches, and clover 
(Fig. 286), 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 proteids. 
Many trees, for example, oaks, beeches, and the cone- 
1 This term is borrowed from the zodlogists as a much simpler one than 
symbionts to express the relation variously known as symbiosis, commensalism, 
or mutualism. 
2 Sarracenia purpurea. 
