372 Mendel's Experiments 



taken into account which are often difficult to define in 

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

 give the forms a peculiar 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 contain very many forms, since the number of the 

 terms, as is known, increases with the number of the 

 differentiating characters as the powers of three. 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 

 two original stocks differ in seven characters, and 100 and 

 200 plants were raised from the seeds of their hybrids to 

 determine the grade of relationship of the offspring, we can 

 easily see how uncertain the decision must become, since 

 for seven differentiating characters the combination series 

 contains 16,384 individuals under 2187 various forms; 

 now one and then another relationship could assert its 

 predominance, just according as chance presented this or 

 that form to the observer in a majority of cases. 



If, furthermore, there appear among the differentiating 

 characters at the same time dominant characters, which 

 are transmitted entire or nearly unchanged to the hybrids, 

 then in the terms of the developmental series that one of 

 the two original parents which possesses the majority of 

 dominant characters must always be predominant. In the 

 experiment described relative to Pisiim, in which three 

 kinds of differentiating characters were concerned, all the 

 dominant characters belonged to the seed parent. Although 

 the terms of the series in their internal composition approach 

 both original parents equally, yet in this experiment the 

 type of the seed parent obtained so great a preponderance 

 that out of each sixty-four plants of the first generation 

 fifty-four exactly resembled it, or only differed in one 

 character. It is seen how rash it must be under such 

 circumstances to draw from the external resemblances of 

 hybrids conclusions as to their internal nature. 



Gartner mentions that in those cases where the develop- 

 ment was regular, among the offspring of the hybrids the 

 two original species were not reproduced, but only a few 

 individuals which approached them. With very extended 



