18431862] FLORAL SYMMETRY 249 



namely, a flower bilaterally different : one other, I observe, has Letter 581 

 half its calyx purple. Is this not very curious, and opposed 

 to the morphological idea that a flower is a condensed con- 

 tinuous spire of leaves ? Does it not look as if flowers were 

 normally bilateral ; just in the same way as we now know 

 that the radiating star-fish, etc., are bilateral ? The case 

 reminds me of those insects with exactly half having secondary 

 male characters and the other half female. 



It is interesting to note his change of view in later years. In an undated 

 letter written to Mr. Spencer, probably in 1873, he says : "With respect 

 to asymmetry in the flowers themselves, I remain contented, from all that 

 I have seen, with adaptation to visits of insects. There is, however, 

 another factor which it is likely enough may have come into play viz., 

 the protection of the anthers and pollen from the injurious effects of 

 rain. I think so because several flowers inhabiting rainy countries, as 

 A, Kerner has lately shown, bend their heads down in rainy weather." 



To J. D. Hooker. Letter 582 



June [1855]. 



This is an early example of Darwin's interest in the movements of 

 plants. Sleeping plants, as is well known, may acquire a rhythmic 

 movement differing from their natural period, but the precise experiment 

 here described has not, as far as known, been carried out. See Pfeffer, 

 PeriodiscJie Beuuegimgen, 1875, p. 32. 



I thank you much for Hedysarum : I do hope it is not very 

 precious, for, as I told you, it is for probably a most foolish 

 purpose. I read somewhere that no plant closes its leaves 

 so promptly in darkness, and I want to cover it up daily for 

 half an hour, and see if I can teach it to close by itself, or 

 more easily than at first in darkness. I am rather puzzled 

 about its transmission, from not knowing how tender it is. ... 



To J. D. Hooker. Letter 583 



Down, July I9th, 1856. 



I thank you warmly for the very kind manner with which 

 you have taken my request. It will, in truth, be a most 

 important service to me ; for it is absolutely necessary that I 

 should discuss single and double creations, as a very crucial 

 point on the general origin of species, and I must confess, 

 with the aid of all sorts of visionary hypotheses, a very hostile 

 one. I am delighted that you will take up possibility of 

 crossing ; no botanist has done so, which I have long 



