DISCUSSION OF DEPENDENT PLANTS 373 



are cared for by the ants, and the latter secure the honey dew 

 as food. Throughout the summer and autumn the ants con- 

 stantly care for the aphids and their young. Aphid eggs are 

 carried to places most favorable for their hatching, and when 

 the young are hatched they are transplanted upon tender 

 young roots. When disturbances of the soil threaten destruc- 

 tion to the eggs, the ants seize them as they would their 

 own eggs and carry them away. At the beginning of the 

 winter aphid eggs are carried by the ants into the deepest 

 parts of the ant nests. At the return of favorable weather 

 the eggs are brought forth again to suitable places for hatch- 

 ing. In this case the aphids which are parasitic upon the 

 corn roots are themselves in slavery (Jielotism) to the ants, 

 and this interrelation obviously reaches a high degree of 

 development. 



In connection with the corn plant, therefore, we have an 

 illustration of six kinds of food relations: (1) the corn is a 

 so-called independent plant, since it is able to manufacture 

 carbohydrate food from water and carbon dioxide ; (2) men 

 and domesticated animals are more or less dependent upon 

 the surplus food that is made by the corn plant and stored in 

 its seeds or in its stalk; (3) living upon corn there is often 

 found the plant parasite known as corn smut ; (4) aphids are 

 placed upon corn roots by ants, the aphids being parasites 

 upon the corn ; (5) the aphids are themselves in a condition 

 of slavery to the ants ; (6) after death the corn plant may be 

 attacked by bacteria and molds, which as saprophytes assist 

 in bringing about its decay. 



There are other destructive plants and animals which may 

 attack the corn plant, but these will not now be discussed. 

 Indeed, almost every kind of plant may be attacked by sev- 

 eral kinds of dependent organisms. One kind of dependency 

 may grade into another, as when a tree-destroying fungus 

 takes its food from a living tree, and after the tree's death 

 continues to live upon the dead body, thus changing from 

 parasitism to saprophytism. 



