REVIEWS. 
409 
explained as follows by Mr. Darwin : — “ The pollen,” he says, a adheres to any 
thin object which is inserted into a flower. The anthers in the one form stand 
nearly, but not exactly, on a level with the stigma of the other ; for the 
distance between the anthers and stigma in the short-styled form is greater 
than that in the long-styled, in the ratio of 100 to 90. This difference is 
the result of the anthers in the long-styled form standing rather higher in 
the tube than does the stigma in the short-styled, and this favours their 
pollen being deposited on it. It follows from the position of the organs 
that if the proboscis of a dead humble-bee, or a thick bristle or rough 
needle, be pushed down the corolla, first of one form and then of the other, 
as an insect would do in visiting the two forms growing mingled together, 
pollen from the long-stamened form adheres round the base of the object, 
and is left with certainty on the stigma of the long-styled form ; whilst 
pollen from the short stamens of the long-styled form adheres a little way 
above the extremity of the object, and some is generally left on the stigma 
of the other form.” That the two kinds of pollen are thus segregated in 
Nature was proved by microscopic examination of that adhering to the pro- 
boscides of the humble-bees and moth caught in the act of visiting the 
flowers, “ and thus,” says Mr. Darwin, “pollen will be regularly carried from 
the one form to the other, and they will reciprocally fertilize one another.” 
Nevertheless, the pollen may occasionally reach the stigma even of the 
flower in which it was produced, and this seems to be especially the case with 
the short-styled form, in which Mr. Darwin found that when he “ inserted 
a bristle or other such object into the corolla of this form, and had, there- 
fore, to pass it down between the anthers seated round the mouth of the 
corolla, some pollen was almost invariably carried dow^ and le f t on the 
stigma.” By this means, and also by the visits of minute insects, such as 
Thrips, crawling into the tube of the flowers, a certain amount of self-im- 
pregnation is therefore possible ; and indeed Mr. Darwin supposes this to 
have taken place in his early experiments in covering these plants, when, as 
already stated, the short-styled individuals produced a minute quantity of 
seed. 
By a series of experiments in the fertilization of the stigmas of the two 
kinds of flowers by pollen from flowers of their own and of the opposite 
form, Mr. Darwin arrived at results which show clearly enough that the 
purpose of this peculiar arrangement of the parts is the assurance of cross- 
fertilization. He says “four essentially different unions are possible ; 
namely, the fertilization of the stigma of the long-styled form by its own- 
form pollen, and by that of the short-styled ; and the stigma of the short- 
styled form by its own-form pollen, and by that of the long-styled,” the 
fecundation of the stigma by its own-form pollen being regarded by Mr. 
Darwin as an “ illegitimate union,” and by that of the other form as a “ legiti- 
mate union,” in accordance with the hypothesis which he had formed (see fig. 
2). The tables showing the results of his experiments bear out his prevision in 
a remarkable manner. From them it appears that in the “ legitimate ” unions 
77 per cent., in the “ illegitimate ” only 45 per cent, of the flowers fer- 
tilized produced capsules ; 92‘6 per cent, of the former and only 69 per 
cent, of the latter being what Mr. Darwin calls good capsules ; that is to 
say, capsules containing more than one or two seeds ; and the superior 
NEW SERIES, VOL. I. — NO. IV. E E 
