in Hybridisation 85 



approached, .some the one and some the other, original 

 stock, or they all incline more to one or the other side ; 

 while with others they remain perfectly like the hybrid and 

 continue constant in their offspring. The hybrids of varieties 

 behave like hybrids of species, but they possess greater varia- 

 bility of form and a more pronounced tendency to revert to 

 the original type. 



With regard to the form of the hybrids and their 

 development, as a rule an agreement with the observations 

 made in Pisum is unmistakable. It is otherwise with the 

 exceptional cases cited. Gartner confesses even that the 

 exact determination whether a form bears a greater resem- 

 blance to one or to the other of the two original species 

 often involved great difficulty, so much depending upon 

 the subjective point of view of the observer. Another 

 circumstance could, however, contribute to render the 

 results fluctuating and uncertain, despite the most careful 

 observation and differentiation; for the experiments plants 

 were mostly used which rank as good species and are 

 differentiated by a large number of characters. In addition 

 to the sharply defined characters, where it is a question of 

 greater or less similarity, those characters must also be 

 taken into account which are often difficult to define in 

 words, but yet suffice, as every plant specialist knows, to 

 give the forms a strange appearance. If it be accepted 

 that the development of hybrids follows the law which is 

 valid for Pisum, the series in each separate experiment 

 must embrace very many forms, since the number of the 

 components, as is known, increases with the number of 

 the differentiating characters in cubic ratio. With a 

 relatively small number of experimental-plants the result 

 therefore could only be approximately right, and in single 

 cases might fluctuate considerably. If, for instance, the 



