Miscellaneous Papers. 391 



The prerequisite in all work of this character consists in the 

 operator or student having series of animals or plants of known 

 lineage. Many species or forms occur in such manner in nature 

 that no uncertainties as to ancestry or purit}^ of strain exists, but 

 in cases where closely related species inhabit the same area or are 

 close neighbors, the possibilities of inter- crossing are to be taken 

 into account. The problem awaiting the investigator may demand 

 a pure strain, a hybrid mixture, or a collective species including 

 two or more elementary species, races, or biotypes ; but in any case, 

 it is absolutely necessary that the nature of the immediate ancestry 

 of the organism be definitely determined. The derivation and 

 composition of a group having been ascertained, they and the suc- 

 cessive generations arising from them must be grown under measur- 

 able conditions of soil and climate, and under known possibilities 

 of hybridization, self-out- and cross fertilization. In other words, 

 the characters or qualities, the behavior and action of which are 

 being tested, must be known as to their composition, purity or com- 

 bination, exactly as the chemist must deal with substances of known 

 constituency in his exacter work. This is the essence of the pedi- 

 gree-culture. 



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

 ties or single characters that progress in research upon evolution 

 must be based; no longer are we concerned with the origination of 

 species, except as an easy generalization; species themselves are so 

 diverse in their composition and aspects among plants, especially, 

 that it might be said with justification that there are almost as 

 many kinds of species as there are numbers of genera. Evolution 

 concerns variations, accretions, diminutions, appearances or disap- 

 pearances of qualities, and it is to these manifestations that our 

 attention is now primarily directed, in the hope of advancing what 

 has now become an exact science. 



Having the unit character as a workable idea and with the power 

 to manipulate examples of it in hybrids in which alternate inherit- 

 ance may occur, it is obvious that widened opportunities are 

 afPorded for studies in the mechanism of heredity, especially in the 

 fortunate instances in which the two components of a hybrid are 

 characterized by the number, form size, or behavior of the chromo- 

 somes. Some light is also being thrown upon the problem of the 

 physical basis of inheritance. 



In a brief paraphrase of the principal ideas presented in this 

 sketch, it is to be said that Darwinism, which has so profoundly 

 affected human thought, and is without parallel so far as importance 



