SUPPLEMENT I 



PART OF A LETTER 



(1867) 



from 



GREGOR MENDEL 



to 



C. NAGELI 



Highly esteemed Sir: 



My most cordial thanks for the printed matter you have so kindly sent me! 

 The papers "die Bastardbildung im Pflanzenreiche," "liber die abgeleiteten 

 Pflanzenbastarde," "die Theorie der Bastardbildung," "die Zwischenformen 

 zwischen den Pflanzenarten," "die systematische Behandlung der Hieracien 

 riicksichtlich der Mittelformen und des Umfangs der Species," especially cap- 

 ture my attention. This thorough revision of the theory of hybrids according 

 to contemporary science was most welcome. Thank you again! 



With respect to the essay which your honor had the kindness to accept, I 

 think I should add the following information: the experiments which are dis- 

 cussed were conducted from 1856 to 1863. I knew that the results I obtained 

 were not easily compatible with our contemporary scientific knowledge, and 

 that under the circumstances publication of one such isolated experiment was 

 doubly dangerous; dangerous for the experimenter and for the cause he repre- 

 sented. Thus I made every effort to verify, with other plants, the results ob- 

 tained with Pisum. A number of hybridizations undertaken in 1863 and 1864 

 convinced me of the difficulty of finding plants suitable for an extended series 

 of experiments, and that under unfavorable circumstances years might elapse 

 without my obtaining the desired information. I attempted to inspire some 

 control experiments, and for that reason discussed the Pisum experiments 

 at the meeting of the local society of naturalists. I encountered, as was to be 

 expected, divided opinion; however, as far as I know, no one undertook to 



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