14 



THE AMERICAN NATURALIST [Vol. XLII 



reproduction from one plant to another. They are closely 

 simulated by some parasites in their manner of attach- 

 ment to the host, but there are radical differences be- 

 tween parasitic attachment and horticultural grafting. 



The two incremental divisions of every normal pheno- 

 gam consists of an epitropic, and an apotropic 3 portion, 

 respectively, separated by the tropaxis. The epitropic 

 portion, beginning with the radicle at germination, enters 

 the ground, divides into roots and rootlets, and estab- 

 lishes the plant in position. This is primary epitropism. 

 The apotropic portion at the same time extends upward, 

 forming the stem and finally the branches, leaves and 

 fruit. This is primary apotropism. The tropaxis is a 

 theoretical disc at, or a transverse section of, the base 

 of the stem from which growth proceeds in opposite di- 

 rections. Its functional existence as a dividing plane is 

 real and constant during the life of the plant, but it is 

 structurally not clearly definable. That is, no material 

 change of plant-texture occurs at the place where the 

 upward and downward growth diverge, and no obstruc- 

 tion to the flow of food-sap from one to the other portion 

 exists there. Suckers, stolons, sprouts, etc., sometimes 

 spring from roots, root-stalks or tubers, and become new 

 plants. This is secondary apotropism. Roots or root- 

 lets often spring from the stem or branches. This is 

 secondary epitropism. A new or secondary tropaxis is 

 formed in every case of secondary apotropism at the place 

 where the upward growth begins and new roots turn down 

 into the soil. 4 



Such are the leading structural characteristics of nor- 

 mal phenogamous plants, which constitute the mass of 



