124 



The Plant World 



A pre-requisite in all work in heredity consists in the opera- 

 tor having an accurate knowledge of the constituency and breed- 

 ing habits of the strains of plants or animals with which he is 

 dealing. Many species consist of a single individible strain 

 occurring alone in nature, but on the other hand a large number 

 include several elementary species or component strains, which 

 may or may not intercross when grown in contiguity. Further- 

 more, the liability to hybridization may be extended so that 

 major species not too closely related, may cross-fertilize, while 

 bi-generic hybrids are recognized. The ancestry and breeding 

 habits of the material being known to the experimenter, he 

 may then proceed to study its transmissal of qualities from 

 generation to generation under measureable conditions of soil 

 or climate. 



This is the essence of the pedigree-culture, and a few 

 writers af academic habit decry its use, upon the ground that it 

 is dealing with organisms under cultivation or artificial condi- 

 tions. In fact it makes possible an exact study of the single 

 qualities or characters of a plant or animal, with respect to their 

 composition, purity, reaction in combination, precisely as the 

 chemist deals with substances of known constituency in his 

 exacter work. The physical elements rarely occur in a* pure 

 state, yet we are far past the stage in which we would object to 

 the use of pure chemicals in researches, in which also the possi- 

 bilities of impurity are taken strictly into account. So with 

 the biologist, having tested the reactions of the qualities being 

 studied under isolated conditions, his next step includes the 

 consideration of their behavior when the plant bearing them is 

 thrown into the closest contact with other organisms with which 

 it might react or have breeding relations. Here, as in chemistry, 

 the data obtained by the study of pure elements will afford 

 the safest guide in the interpretation of the hereditary mani- 

 festations of the organism, or the final character of its con- 

 stituents. When these facts are fully understood, it becomes 

 plain at once that the adverse criticisms of the pedigreed culture 

 in researches upon evolution are contentions, not arguments. 



It has become plainly evident that it is upon the idea of 

 qualities or single characters that progress in research upon 

 evolution must be based; no longer are we concerned with the 



