i860.] ON PLANTS OF THE SAME SPECIES.' 471 



" On the Sexual Relations of the Three Forms of Lythrum 

 salicaria" Ibid. 1864. 



"On the Character and Hybrid-like Nature of the Off- 

 spring from the Illegitimate Unions of Dimorphic and Tri- 

 morphic Plants." Ibid. 1869. 



" On the Specific Differences between Primula veris, Brit. 

 Fl. (var. officinalis, Linn.), P. vulgaris, Brit. Fl. (var. acaulis, 

 Linn.), and P. elatior, J acq. ; and on the Hybrid Nature of 

 the Common Oxlip. With Supplementary Remarks on Nat- 

 urally Produced Hybrids in the Genus Verbascum." Ibid. 

 1869. 



The following letter shows that he began the work on 

 heterostyled plants with an erroneous view as to the meaning 

 of the facts.] 



C. Darwin to J. D. Hooker. 



Down, May 7 [i860]. 

 .... I have this morning been looking at my experi- 

 mental cowslips, and I find some plants have all flowers with 

 long stamens and short pistils, which I will call " male plants," 

 others with short stamens and long pistils, which I will call 

 "female plants." This I have somewhere seen noticed, I 

 think by Henslow ; but I find (after looking at my tw r o sets 

 of plants) that the stigmas of the male and female are of 

 slightly different shape, and certainly different degree of 

 roughness, and what has astonished me, the pollen of the 

 so-called female plant, though very abundant, is more trans- 

 parent, and each granule is exactly only f of the size of the 

 pollen of the so-called male plant. Has this been observed ? 

 I cannot help suspecting [that] the cowslip is in fact dioecious, 

 but it may turn out all a blunder, but anyhow I will mark with 

 sticks the so-called male and female plants and watch their 

 seeding. It would be a fine case of gradation between an 

 hermaphrodite and unisexual condition. Likewise a sort of 

 case of balancement of long and short pistils and stamens. 

 Likewise perhaps throws light on oxlips. . . . 



