Ch. XVI.] FERTILISATION OP FLOWERS. 301 



the problem of evolution is curious, and could hardly have 

 been predicted. Moreover, it was not a permanent bond. My 

 father proved by a long series of laborious experiments, that 

 when a plant is fertilised and sets seeds under the influence of 

 pollen from a distinct individual, the offspring so produced are 

 superior in vigour to the offspring of self-fertilisation, i.e. 

 of the union of the male and female elements of a single 

 plant. When this fact was established, it was possible 

 to understand the raison d'etre of the machinery which insures 

 cross-fertilisation in so many flowers ; and to understand how 

 natural selection can act on, and mould, the floral structure. 



Asa Gray has well remarked with regard to this central idea 

 (Nature, June 4, 1874) : — " The aphorism, ' Nature abhors a 

 vacuum,' is a characteristic specimen of the science of the 

 middle ages. The aphorism, * Nature abhors close fertilisa- 

 tion/ and the demonstration of the principle, belong to our age 

 and to Mr. Darwin. To have originated this, and also the 

 principle of Natural Selection .... and to have applied these 

 principles to the system of nature, in such a manner as to make, 

 within a dozen years, a deeper impression upon natural history 

 than has been made since Linnaeus, is ample title for one man's 

 fame." 



The flowers of the Papilionace© * attracted his attention 

 early, and were the subject of his first paper on fertilisation.^ 

 The following extract from an undated letter to Asa Gray 

 seems to have been written before the publication of this paper, 

 probably in 1856 or 1857 :— 



". ... What you say on Papilionaceous flowers is very 

 true ; and I have no facts to show that varieties are crossed ; 

 but yet (and the same remark is applicable in a beautiful way 

 to Fumaria and Dielytra, as I noticed many years ago), I must 

 believe that the flowers are constructed partly in direct relation 

 to the visits of insects ; and how insects can avoid bringing 

 pollen from other individuals I cannot understand. It is really 

 pretty to watch the action of a humble-bee on the scarlet 

 kidney bean, and in this genus (and in Lathyrw grandiflorus) J 

 the honey is so placed that the bee invariably alights on that 

 one side of the flower towards which the spiral pistil is pro- 

 truded (bringing out with it pollen), and by the depression of 



* The order to which the pea and bean belong. 



t Gardener? Clironicle, 1857, p. 725. It appears that this paper was 

 a piece of " over-time " work. He wrote to a friend, " that confounded 

 Leguminous paper was done in the afternoon, and the consequence was I 

 had to go to Moor Park for a week." 



X The sweet pea and everlasting pea belong to the genus Lathyrus. 



