1 877.] ON PLANTS OF THE SAME SPECIES.' 309 



fertilised by insects, and are in this case abundantly crossed ; 

 but that the flowers are not always, especially in early spring, 

 visited enough by insects, and therefore the little imperfect 

 self-fertilising flowers are developed to ensure a sufficiency of 

 seed for present generations. Viola canina is sterile, when 

 not visited by insects, but when so visited forms plenty of 

 seed. I infer from the structure of three or four forms of Bal- 

 saminecz, that these require insects ; at least there is almost 

 as plain adaptation to insects as in Orchids. I have Oxalis 

 acetosella ready in pots for experiment next spring ; and I 

 fear this will upset my little theory. . . . Campaiiula carpa- 

 thica, as I found this summer, is absolutely sterile if insects 

 are excluded. Specularia speculum is fairly fertile when 

 enclosed ; and this seemed to me to be partially effected by 

 the frequent closing of the flower ; the inward angular folds 

 of the corolla corresponding with the clefts of the open 

 stigma, and in this action pushing pollen from the outside of 

 the stigma on to its surface. Now can you tell me, does S. 

 perfoliata close its flower like >S. speculum, with angular inward 

 folds ? if so, I am smashed without some fearful " wriggling." 

 Are the imperfect flowers of your Specularia the early or the 

 later ones ? very early or very late ? It is rather pretty to 

 see the importance of the closing of flowers of ^. speculum. 



['Forms of Flowers' was published in July 1877; in 

 June he wrote to Professor Carus with regard to the 

 translation : — 



" My new book is not a long one, viz. 350 pages, chiefly of 

 the larger type, with fifteen simple woodcuts. All the proofs 

 are corrected except the Index, so that it will soon be 

 published. 



" . . . . I do not suppose that I shall publish any more 

 books, though perhaps a few more papers. I cannot endure 

 being idle, but heaven knows whether I am capable of any 

 more good work." 



