Hereditary Characters Are Units 27 



without difficulty, in the latent state. In truth, the prin- 

 ciple illustrated by this example holds good also in the 

 phenomena of monoecism and dioecism, of the di- and 

 trimorphism of flowers, and indeed, throughout the en- 

 tire range of organ-formation. Everywhere we find 

 characteristics which cannot exist simultaneously in the 

 same organ, and yet must be associated in a latent state 

 during its youth. 



In summarizing briefly what has been said, we see 

 that experiments and observations on the origin and fix- 

 ing of variations teach us to recognize hereditary char- 

 acters as units with which we can experiment. They 

 teach us further that these units are miscible in almost 

 every proportion, most experiments really amounting 

 merely to a change in this proportion. 



The above considerations are verified in a striking 

 manner by experiments in hybridization and crossing. In 

 no other connection does the concept of a species as a 

 unit made up of independent factors stand forth so 

 clearly. Everyone knows that the hereditary characters 

 of two parents may be mixed in a hybrid. And the ex- 

 cellent experiments of many investigators have taught us 

 how, in the descendents of hybrids, an almost endless 

 variation can usually be observed, which is essentially due 

 to a mixing of the characteristics of the parents in a most 

 varied manner. 



The hybrids of the first generation have quite definite 

 characteristics for each pair of species. If one produces 

 a hybrid of two species, which previous investigators have 

 already succeeded in crossing, he can, as a rule, rely on 

 the description given of it tallying exactly with the newly 

 produced intermediate form. If the hybrid is fertile 

 without the help of its parents, and if its progeny are 



