338 PLANT HYBRIDIZATION BEFORE MENDEL 



with Zea and Matthiola, and finally also with Lilium. In this connection 

 the advantages of Pisum naturally made themselves at once noticeable, 

 especially the great convenience of the investigations, which, indeed, 1 

 could only carry on accessorily. 



"To one of my most fruitful objects of research, Mirabilis jalapa, 

 I also first came indirectly, when I investigated (1907) the influence 

 which the; number of pollen grains used for pollination has upon the 

 progeny. I had originally, indeed, not at all overlooked the matter of 

 studying the behavior of the progeny in further generations, but had 

 proceeded from other bases of inquiry. 



"Besides through Focke's book, I had been made cognizant of Mendel's 

 investigations through my teacher Nageli. And I believe also to remem- 

 ber that he told me of Mendel, but certainly only of the Hieracium 

 investigations, in which alone he was permanently interested. Some- 

 thing of them was known to me also from the theoretical introduction 

 to the first volume of the Hieracium monograph of Nageli and Peter, 

 and from Nageli's introduction to the Primula monograph of E. Widmer. 

 The memoir of Mendel on his Hieracium hybrids I first read, however, 

 • with that on the peas hybrids, in the autumn of 1899. Nageli was, at 

 the time when I became his pupil, already in ill health, read none of 

 his colleagues' works any longer, and likewise no longer conducted his 

 practicum any more. He interested me in the structure and growth of 

 the vegetable cell membrane. When I began the genetic researches (1891), 

 he was already dead. The above-cited references to Mendel, and indeed 

 also the recollection of the verbal mention of Mendel, prompted me 

 to ask Nageli's family for possible letters received. His scientific corre- 

 spondence was, however, not to be found at that time. It first came to 

 light through an accident in 1904. The letters of Mendel were sent to 

 me by the family, and were published by me ; the remaining scientific 

 correspondence the family then destroyed." 



In Die Naturwissenschaften, lOth Jahrgang, Heft 29, pp. 

 623-31 (July 21, 1922), a number devoted to papers in memory 

 of Gregor Mendel, on the one hundredth anniversary of his 

 birth, Professor Correns contributed an article entitled, "Etwas 

 iiber Gregor Mendels Leben und Wirken." In the course of this 

 article (p. 630), Correns reports as follows. His comments are 

 herewith introduced as supplementary to the letters quoted above : 



"Through experiments in xenia formation, I have had my attention 

 directed to the behavior of hybrids in maize and peas races. The in- 

 vestigations, however, could only be carried on slowly, in a certain de- 

 gree as side issues, through years, together with the other work, so that 

 I was already able to propound, in the first contribution on Pisum 

 sativum, a genealogical tree up to the fourth generation inclusive. I had 

 soon come to the counting-out stage, and also to the correct explanation, 

 when for the first time I looked through the literature, and found that 

 my results were not new. Focke says on the subject of Pisum in his 

 'Pflanzenmischlinge' (1881) that Mendel's numerous peas crosses gave 



