88 Cooh — Hybrids and Mutations. 



induce a parthenogenetic develojmient which was widely re- 

 })orted two or three j^ears ago as "artificial fertilization.'' 



Cross-fertilization and self-fertility, like most terms, are rela- 

 tive. Many plants have been accounted self-fertile because they 

 can propagate without crossing for a few generations. Thus 

 Wallace has suggested that widely distributed plants are self- 

 fertile, the stimulation of new conditions serving, as it were, as 

 a substitute for crossing. This is doubtless true within limits, 

 but should not be taken to mean that complete autogamy is 

 maintained in this manner.* The effects of new substances and 

 new external conditions, while perhaps to be best understood 

 from the evolutionary standpoint, have not the evolutionary 

 significance often ascribed to them, since the increased vigor 

 and other modifications obtained are neither permanent nor 

 hereditary. 



Perhaps for lack of a rational explanation of the known 

 benefits of change of descent or of external conditions, both 

 agriculture and medicine are still practiced largely on the 

 theory that there is some particular food, tonic, fertilizer, or 

 climatic treatment which is l)est for each plant, animal, or dis- 

 ease. When it is appreciated that even the best is best only 

 while it is recent or new, kinetic systems of farming, feeding, 

 and curing may be elaborated, which shall increase agricultural 

 ))roductiveness and human health b}'' properly determined suc- 

 cessions or alternations of diets, tonics, climates, or soils. The 

 rotation of crops, the interchange of seed between different 

 regions, the application of fertilizers, and the breeding of new 

 varieties, more vigorous and resistant, are different methods of 

 attaining the same practical results, and the utility of the sev- 

 eral expedients ma}^ be found to rest on a single l)iological law. 



The vegetative vigor of hybrids and mutations is not a 

 difficulty, then, in a kinetic theory of evolution, but affords 

 a strongl}'' corroborative series of phenomena. The defective 

 reproduction is the abnormal fact, and this appears to be defi- 

 nitely associated with a lack of normal interbreeding. The 

 organism may be prospered in its growth by any change not 



*Mr. Swingle suggests also that the heteroecisiu of the parasitic rnst- 

 fungi may be a phenomenon of the same kind. Tlie diverse forms which 

 the same rust assumes on its ditierent hosts may he looked upon as a 

 further adaptive substitute for interbreeding. 



