412 
POPULAR SCIENCE REVIEW. 
Primulacese. In this plant the flowers are trimorphic ; that is to say, they 
exhibit three different proportions of the style and stamens. We have long- 
styled, mid-styled, and short-styled flowers, and each of these forms contains 
stamens of two different lengths (see fig. 3). In the long-styled form the style 
projects far beyond the six long stamens, which are of middle length, corres- 
ponding in this respect with the pistil of the mid-styled form, and protrude, 
with the style, from the mouth of the flower ; within the flower are six short 
stamens. In the mid-styled flowers the six long stamens are about as long 
as the style in the long-styled form, with the longest stamens in which the 
style corresponds in length, and the short stamens are again enclosed within 
the calyx. The short-styled flowers have the pistil entirely concealed 
within the flower, whilst both sets of stamens project from its opening 
and are respectively of the length of the longest stamens in the other 
two forms. By a series of experiments, far too complicated for us to attempt 
to give any account of them here, Mr. Darwin ascertained that the pollen 
from each of the three kinds of stamens is destined to fertilize the pistil of 
corresponding length ; the fertility of the legitimate unions on this principle, 
(t as judged by the proportion of the fertilized flowers which yielded cap- 
sules, is as 100 to 33; and judged by the average number of seeds per 
capsule as 100 to 46.” But taking the average number of seeds per flower 
fertilized, the proportional fertility is as 71 ‘89 to 11*03. As Mr. Darwin 
indicates, the peculiar arrangements of the parts in this plant also are 
specially adapted to the requirements of fertilization by the agency of 
insects. 
Several other trimorphic species are noticed here, and the details of 
exneriments made upon them tabulated. The experiments and tables are 
necessarily of a somewhat complicated description, seeing that in the case of 
a trimorphic plant of this kind six legitimate and twelve illegitimate unions 
are possible, and all these had to be tried in order to get at reliable results. 
Side by side with these elaborate provisions for securing cross-fertiliza- 
tion it is somewhat singular to find that in some species of plants there 
prevails a dimorphism which serve a directly opposite purpose. A con- 
siderable number of plants (Mr. Darwin here gives a list of fifty-five genera 
including them) bear what have been called cleistogamic flowers, which 
never open at all, are more or less imperfect in their structure, and yet bear 
an abundance of seed by a process of self-fertilization. The object of this 
peculiar arrangement, which may be observed in common species of Viola , 
in the woodsorrel, and many other well-known plants, is, according to the 
author, the production of u an abundant supply of seeds with little expen- 
diture ; ” and he adds, “we can hardly doubt that they have had their 
structure modified and degraded for this special purpose ; perfect flowers 
being still almost always produced, so as to allow of occasional cross- 
fertilization,” which he has proved to be possible. In some instances, also, 
of which one is furnished by the pansy (Viola tricolor), there are two forms 
of flowers, one much more conspicuous than the other, and adapted to cross- 
fertilization by insects ; whilst the smaller flowers, although not closed, like 
cleistogamic flowers, are more or less modified to insure self-fertilization. 
In these cases the two forms of flowers are produced upon distinct plants. 
Mr. Darwin’s researches upon what he calls the illegitimate offspring of 
