22 MASSACHUSETTS HORTICULTURAL SOCIETY. 



- The combined action of the laws of heredity and variation have 

 been the means then of bringing about the evolution of fruit plants ; 

 their characteristics are due to the influences to which they have 

 been exposed, while their present forms exist through the survival 

 of the fittest relations ; they depend very much for existence on their 

 environment, in which changes occur without any preparation for 

 them and when very great result in the death of the plant. This 

 consideration leads us to notice that many fruit plants subject to 

 health and disease are dependent on many and complicated 

 conditions which are bej'ond our control, while others are acces- 

 sible and capable of being modified by our actions. A fruit tree 

 is a chemical laboratory in constant action ; its physical or 

 chemical properties, diversely modified, underlie nutrition, growth 

 and reproduction ; and it is constituted of substances more or less 

 fluid and solid which hold in solution salts and gases. Atoms of 

 atmospheric origin constantly mingling with the organic molecules 

 are separating them, and would destroy the tree if food had not 

 been introduced from without into its texture ; which renovating 

 substances, after having undergone preparatory chemical changes 

 and become nutriments, are assimilated b^^ the trees. Complicated 

 unions with other elements are formed by carbon, whence arise 

 the first and most indispensable basis of all vital phenomena, the 

 albuminous combinations. 



There is something in the surrounding circumstances in which 

 a fruit plant is placed that is the most probable stimulant of 

 change of its character, because it is entirely dependent on 

 terrestrial forces for its sustenance and preservation. The 

 difficulty has been to connect these movements with change of 

 structure ; and all we can assume is, that those plants whose 

 changed organization gave them an advantage over those not so 

 favored, have survived and transmitted their modifications. 

 Sometime we must expect to have a science of life that will tell us 

 why some fruit plants have died out and others have survived ; 

 while now only the fact is established, that health, disease, and 

 death sooner or later take place ; after an allotted period the tree 

 ceases to perform its proper functions ; it remains primitive or 

 unchanged ; it progresses or retrogresses. Periods of growth, of 

 bloom, and of decay will exist, which decadence is degeneration, 

 not dissolution, when applied to species : while the cause of the 

 transportation is not deterioration, but adaptation or modification 

 by the aid of external formative forces. 



