1 862.] 



ON PLANTS OF THE SAME SPECIES. 



301 



a plan (which however never went beyond an early stage of 

 discussion) of employing him to work out certain problems 

 connected with intercrossing. 



The following letter refers to my father's investigations 

 on Lythrum,* a plant which reveals even a more wonderful 

 condition of sexual complexity than that of Primula. For 

 in Lythrum there are not merely two, but three castes, 

 differing structurally and physiologically from each other :] 



C. Darwin to Asa Gray, 



Down, August 9 [1862]. 



My dear Gray, — It is late at night, and I am going to 

 write briefly, and of course to beg a favour. 



The Mitchella very good, but pollen apparently equal- 

 sized. I have just examined Hottonia, grand difference in 

 pollen. Echium vulgare, a humbug, merely a case like 

 Thymus. But I am almost stark staring mad over Lythrum ;f 

 if I can prove what I fully believe ; it is a grand case of 

 TRIMORPHISM, with three different pollens and three stigmas ; 

 I have castrated and fertilised above ninety flowers, trying all 

 the eighteen distinct crosses which are possible within the 

 limits of this one species ! I cannot explain, but I feel sure 

 you would think it a grand case. I have been writing to 

 Botanists to see if I can possibly get L. hyssopi '.folia, and it has 

 just flashed on me that you might have Lythrum in North 

 America, and I have looked to your Manual. For the love 



* He was led to this, his first 

 case of trimorphism, by Lecoq's 

 ' Geographie Botanique,' and this 

 must have consoled him for the 

 trick this work played him in turn- 

 ing out to be so much larger than 

 he expected. He wrote to Sir J. 

 D. Hooker : " Here is a good joke : 

 I saw an extract from Lecoq, ' Gdo- 



graph. Bot.,' and ordered it and 

 hoped that it was a good sized 

 pamphlet, and nine thick volumes 

 have arrived ! " 



t On another occasion he wrote 

 (to Dr. Gray) with; regard to Lyth- 

 rum : " I must hold hard, other- 

 wise I shall spend my life over 

 dimorphism." 



