170 American Horticultural Society. 



imcti'on with which it is connected. The results are far-reaching, and indi- 

 rectly involve other processes; as, for example, exclusion of iron would lirst 

 of all result in failure of chlorophyl formation. Through this, however, 

 starch and sugar would fail to form; the entire process of assimilation and 

 nutrition would be disturbed; the respiration would become abnormal; the 

 growth would become of a weak and succulent nature, and the whole plant 

 w'ould soon be brought into a condition which would make it the ready prey 

 of parasitic growths, until it finally succumbed to death. We are thus led 

 to see that we may have degrees of special or general debility corresponding 

 to the degree in which the requirements of growth are met. Complete nu- 

 trition is an essential basis of health, and any deviation from it must result 

 in arrest of function in some one or more directions. 



Looking yet further to the causes which induce disease, we observe that 

 ■cultivation at the hands of man exerts a well defined influence, which is 

 manifested in a great variety of ways, and may be generally illustrated by 

 functional and chemical changes. 



It is well known, that under certain conditions plants often exhibit a special 

 activity in one direction of development, to the more or less complete arrest 

 of function in some other direction. This is true in cases where the power 

 of vegetative reproduction through bulbs, offsets, etc., becomes largely de- 

 veloped, with a corresponding abortion of the sexual process. The general 

 tendency of cultivation is to excessive vegetation, and not to reproduction ; 

 and conformitj^ to this law is exemplified in the gradual obliteration of seed 

 through conditions of high cultivation, as seen in many of our choicest mod- 

 ern fruits, which retain their abnormal condition just so long as the peculiar 

 circumstances which tended to their development are maintained, but which 

 rapidly revert to their original state when these conditions are withdrawn 

 ■or an attempt is made to propagate through the seed. Furthermore, the pe- 

 culiar conditions of cultivation which force the plant rapidly on to a prema- 

 ture development, bring the whole organism into a condition of unstable 

 equilibrium in which the functions seem to be discharged under a state of 

 ihigh tension, and are not correctly balanced against the adverse influences 

 of environment. This always serves as a predisposing cause of disease, and 

 it is probably safe to say, upon general principles, that the more highly cul- 

 tivated a plant, or the more the vital equilibrium is disturbed by conditions 

 ■of growth, the more susceptible is the organism to disease. 



While thus on the one hand cultivation may tend to induce certain disor- 

 ders, on the other hand it may undoubtedly be capable of promoting certain 

 changes whereby disease is not only warded off, but of inducing definite 

 chemical changes for the permanent enhancement of the economic value of 

 the plant or its parts, especially in those cases where the elements of nutri- 

 tion are wisely controlled. In this connection the results obtained by Dr. 

 Groessman in varying the ash constituents of fruits by cultivation, are most 

 significant. Comparing the ash of the common wild strawberry (Fragaria 



