28 MASSACHUSETTS HORTICULTURAL SOCIETY. 



guishing characteristics from any inherent cause. Neither do 

 varieties propagated by buds and grafts necessaril}' deteriorate 

 and die, although trees propagated only by buds have a weaker 

 hold on life than a series produced from seed. The positive 

 evidence of vigorous old trees bearing sound fruits, is an argument 

 that aged varieties do not wear out except by exhaustion of the 

 soil, incoming of disease, alteration of climate, or other natural 

 circumstances, where failure is manifest. Non-sexually propagated 

 varieties are not endowed with the same unlimited power of 

 duration that is posss&sed by varieties and species propagated by 

 seed. The inference to be derived from the principle that cross- 

 fertilization between the individuals of a species is the plan of 

 Nature is fairly sustained, that no bi-sexual species constantly 

 self-fertilized would continue to exist. If such theoi'ies can be 

 maintained, we must conclude that sexually propagated varieties 

 or races, although liable to disappear through change, need not be 

 expected to wear out and do not ; but that non-sexually propa- 

 gated kinds, though not especially liable to change, may theoreti- 

 cally wear out, yet but slowly. There is a tendency, inherent in 

 species as in individuals, to die out, since no organic being self- 

 fertilizes indefinitely. This is now counteracted by wider sexual 

 breeding, amply secured in nature, which reinforces vitality to 

 such an extent as to warrant the inference, " that some unknown 

 great good is derived from the union of individuals that have 

 kept distinct for generations." 



The phenomena of the life of fruit plants and their structures 

 thus have been formed and produced according to the laws of 

 growth, reproduction, inheritance, and variability. The science 

 of morphology informs us what their manner of organization is ; 

 physiology tells us how they live and the laws of their distri- 

 bution where they are found ; the science of causes how they 

 have come to be what they are. But important problems remain 

 unsolved and modern observers do not yet give an intelligible 

 account of the changes which succeed one another during the 

 growth of the smallest particle of the simplest fruits nor of the 

 mode of origin of the first living matter that formed the plants. 

 Nature only constructs, and scientific men must be allowed to 

 work on in the investigation of the origin of new forms. Fruit 

 evolution so far as now explained seems to take its stand on the 

 rational interpretation of the facts of Nature ; and there is grand- 

 eur in the contemplation of the wonderful and beautiful forms. 



