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POPULAR SCIENCE REVIEW. 
the flower, where it stands, like the head of a pin, far above the level of the 
anthers, which spring from the interior of the tube about half-way down. 
In the u thrum-eyed ” plants, on the contrary, the anthers are placed quite 
in the throat of the flower ; and the style, which is much shorter than in the 
preceding form, only carries the somewhat flattened and much smoother 
stigma about half-way up the tube of the corolla. In other words, the 
relative positions of the anthers and stigmas in the two forms are as nearly 
as possible reversed. For this difference in structure Professor Hildebrand 
long since proposed the term “heterostyled,” which Mr. Darwin retains in 
the present work, although he gives the preference — justly, as it seems to us 
— to the term “ heterogonous ” proposed by Dr. Asa Gray, to express the 
same condition of the reproductive parts. 
There are certain other differences in the two forms. Thus the long- 
styled plants have the pollen-grains smaller than those of the short-styled, 
and of an oblong form, whilst the pollen of the short-styled plants is nearly 
spherical ; and further, the long-styled flowers have larger ovules and pro- 
duce fewer seeds than their short-styled fellows. The two forms of flowers 
never occur upon the same plant, and the long-styled flowers seem to open 
a little earlier than the short-stvled. The short-styled flowers are more 
fertile than the long-styled, the proportion of seed produced being by weight 
nearly as four to three. 
To ascertain the meaning of these curious phenomena, which he naturally 
believed to point towards cross-fertilization, Mr. Darwin instituted a series 
of experiments on the cowslip, the results of which are very interesting. 
He covered with net six plants of the short-stvled and eighteen of the 
long-styled form, and found that they produced respectively twenty-four 
and seventy-four umbels of flowers. The six short-styled plants furnished 
altogether about flfty seeds, weighing 1*3 grain, but not a single seed was 
produced by the eighteen long-styled cowslips. u Judging from the exposed 
plants which grew all round in the same bed,” says Mr. Darwin, u and had 
been treated in the same manner, excepting that they had been exposed to 
the visits of insects, the above six short-styled plants ought to have produced 
ninety-two grains’ weight instead of only T3; and the eighteen long-styled 
plants, which produced not one seed, ought to have produced above two 
hundred grains’ weight. The production of a few seeds by the short-styled 
plants was probably due to the action of Thrips, or of some other minute 
insect.” 
Thus we have insects again brought in as the marriage-priests of plants ; 
and, considering the arrangement of the parts, as already described, in the 
cowslip, it is easy to see in what manner the visits of insects to the flowers 
are made available for this purpose. The flowers of the cowslip and of 
other species of Primula secrete an abundance of nectar, and bees and moths 
may be seen visiting them in search of this sweet food. Mr. Darwin 
records his observation of two species of humble-bees sucking out the nectar 
in a legitimate manner by inserting their trunks through the throat of the 
flower ; Mr. H. Muller has seen an Anthophora and a Bonibylius similarly en- 
gaged ; and one ©f Mr. Darwin’s sons caught Cucullia verbasci in the act. There 
is, indeed, no doubt that insects visit these flowers, and the mode in which 
their agency is made subservient to the fertilization of the different forms is 
