202 EET. G. HENSLOW — FERTILISATION OF PLANTS. 



myself, viz. that of the crocus. As soon as the bees come out in 

 spring, you can easily see how they succeed in intercrossing this 

 plant. The perianth of the crocus is contracted at the base, so 

 that if the bee alights on the inner surface of it, she cannot get 

 down to the bottom where the honey lies, and so she alights on the 

 brush-like stigma, and goes head downwards, grasping the whole 

 column of stamens with her legs ; consequently the anthers dust the 

 bee on the under-side with pollen. It should be noticed that 

 the anthers do not burst inwards, as is ordinarily the case in 

 flowers, but outwards, so that the bee smears herself over with 

 pollen ; she then flies to another flower, alights on the brush-like 

 stigmas, and these of course sweep off the pollen which the bee 

 has brought. That is just an instance of the intercrossing of 

 flowers. Mr. Darwin's work on the 'Fertilisation of Orchids' is a 

 most interesting book, and deals with one particular family ; but 

 intercrossing occurs in nearly all orders of the Vegetable Kingdom. 



Having thus detected that the poUen was necessary to fertilise 

 the pistil, intercrossing was looked upon to some extent as a 

 necessity. It was a sort of general surmise that plants produced 

 by the resulting seeds were benefited if the pollen had come from 

 any other flower than its own ; but the exact value was never 

 known ; and it is remarkable that Dean Herbert, in his work on 

 the AmarylUdece (1836) says: "I am inclined to think I have 

 derived advantage from impregnating the flowers from which I 

 •wish to obtain seeds, from individuals of another variety or another 

 flower rather than its own, and especially of any grown in different 

 soil or aspect." That is a remarkable sentence, and we have been 

 forty years without having this fact established, so that the great 

 value of ilr. Darwin's new book lies in the fact that it gives us the 

 exact value of these three kinds of crossing. 



Let us, then, start from this point, and we will take four kinds 

 of combination. The first is when the pollen of flowers falls on 

 their own stigmas : that is self-fertilisation. The second kind of 

 union is that of crossing different flowers, but on the same plant. 

 The third is the intercrossing plants of the same stock, grown in 

 the same gardi'n, and sprung from the same ancestor, and conse- 

 quently all of close kinship. Lastly, there is the crossing plants from 

 distinct stocks ; one, say, growing in Mr. Darwin's garden, and the 

 other brought from Colchester or elsewhere, and of course grown 

 under dift'erent circumstances. 



Mr. Darwin went through an elaborate series of experiments on 

 fifty-four species of thirty distinct natural orders, and I will give 

 you the main results. The first case upon which he experimented 

 he carried out more fully than all the others. He cultivated the 

 so-called "Convolvulus major" (Ipomaa purpurea) for ten years, year 

 by year, and his method was to fertilise the flowers artificially 

 with their own ])ollen, and collect the seeds from those flowers : he 

 called them "self-fertilised seeds." On the other hand, he fertilised 

 the flowers of ])lants with tlu> pollen of other flowers growing- in his 

 garden, and called the result " intercrossed seeds." Then he 



