GREGOR MENDEL 



repeat the experiments. When, last year, I was asked to publish my lecture 

 in the proceedings of the society, I agreed to do so, after having re-examined 

 my records for the various years of experimentation, and not having been able 

 to find a source of error. The paper which was submitted to you is the un- 

 changed reprint of the draft of the lecture mentioned; thus the brevity of the 

 exposition, as is essential for a public lecture. 



I am not surprised to hear your honor speak of my experiments with mis- 

 trustful caution; I would not do otherwise in a similar case. Two points in 

 your esteemed letter appear to be too important to be left unanswered. The 

 first deals with the question whether one may conclude that constancy of type 

 has been obtained if the hybrid Aa produces a plant A, and this plant in turn 

 produces only A . 



Permit me to state that, as an empirical worker, I must define constancy of 

 type as the retention of a character during the period of observation. My 

 statements that some of the progeny of hybrids breed true to type thus in- 

 cludes only those generations during which observations were made; it does 

 not extend beyond them. For two generations all experiments were conducted 

 with a fairly large number of plants. Starting with the third generation it 

 became necessary to limit the numbers because of lack of space, so that, in 

 each of the seven experiments, only a sample of those plants of the second 

 generation (which either bred true or varied) could be observed further. The 

 observations were extended over four to six generations (p. 13). Of the varieties 

 which bred true (pp. 15-18) some plants were observed for four generations. I 

 must further mention the case of a variety which bred true for six generations, 

 although the parental types differed in four characters. In 1859 I obtained a 

 very fertile descendent with large, tasty, seeds from a first generation hybrid. 

 Since, in the following year, its progeny retained the desirable characteristics 

 and were uniform, the variety was cultivated in our vegetable garden, and 

 many plants were raised every year up to 1865. The parental plants were 

 bcDg and BCdG: 



B. albumen yellow b. albumen green 



C. seed-coat grayish-brown c. seed-coat white 



D. pod inflated d. pod constricted 

 G. axis long g. axis short 



The hybrid just mentioned was BcDG. 



The color of the albumen could be determined only in the plants saved for 

 seed production, for the other pods were harvested in an immature condition. 

 Never was green albumen observed in these plants, reddish-purple flower 

 color (an indication of brown seed-coat), constriction of the pod, nor short 

 axis. 



This is the extent of my experience. I cannot judge whether these findings 

 would permit a decision as to constancy of type; however, I am inclined to 

 regard the separation of parental characteristics in the progeny of hybrids in 

 Pisum as complete, and thus permanent. The progeny of hybrids carries one or 

 the other of the parental characteristics, or the hybrid form of the two; I have 



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