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, w^hich 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 progen}^ are 



