82 
POPULAll SCIENCE REVIEW. 
palaeontology of any formation that we possess, and with the previous 
volumes of Professors Leidy, Cope, and Lesquereux it will materially assist 
in solving one of the most difficult problems in the Geology of Western 
North America, involving the relations of the lignitiferous deposits to the 
well-marked cretaceous rocks underlying them. 
FERTILIZATION OF PLANTS.* 
I T is probably well known to most of our readers that Mr. Darwin many 
years ago was led to the belief that cross-fertilization was a necessary 
process in many, perhaps in most plants, even though the organs of the two 
sexes might be present together in their flowers. The prime agents in 
effecting this he took to be insects, and his own researches on the Orchids, 
the Primulaceae, and some other groups of plants, followed by the investi- 
gations of other naturalists, both in this country and abroad, have gone far 
towards establishing the truth of this generalization. The means by which 
the cross-fertilization of plants, by the contact of the pollen of one flower 
with the stigma of another flower, on the same or a different plant, is pro- 
vided for, are indicated as follows by Mr. Darwin in his lately published book 
on “The Effects of Cross and Self-Fertilization.” He says: “Cross-fertilization 
is sometimes ensured by the sexes being separated, and in a large number 
of cases by the pollen and stigma of the same flower being matured at 
different times. Such plants are called dichogamous, and have been divided 
into two sub-classes : proterandrous species, in which the pollen is mature 
before the stigma, and proterogynous species, in which the reverse occurs ; 
this latter form of dichogamy not being nearly so common as the other. 
Cross-fertilization is also ensured, in many cases, by mechanical contrivances 
of wonderful beauty, preventing the impregnation of the flowers by their 
own pollen. There is a small class of plants, which I have called dimorphic 
or trimorphic, but to which Hildebrand has given the more appropriate 
name of heterostyled ; this class consists of plants presenting two or three 
distinct forms, adapted for reciprocal fertilization, so that, like plants with 
separate sexes, they can hardly fail to be intercrossed in each generation. 
The male and female organs of some flowers are irritable, and the insects 
which touch them get dusted with pollen, which is thus transported to 
other flowers. Again, there is a class in which the ovules absolutely 
refuse to be fertilized by pollen from the same plant, but can be fertilized by 
pollen from any other individual of the same species. There are also very 
many species which are partially sterile with their own pollen. Lastly, 
there is a large class in which the flowers present no apparent obstacle of 
any kind to self-fertilization ; nevertheless these plants are frequently inter- 
crossed, owing to the prepotency of pollen from another individual or variety 
over the plant’s own pollen.” 
The wonderful variety of arrangements all tending towards the same end, 
so admirably summed up in the preceding paragraph, is sufficient, as Mr. 
* 11 The Effects of Cross and Self-Fertilization in the Vegetable Kingdom.” 
By Charles Darwin, M.A., F.R.S., &c. London : John Murray. 1876. 
