Fertilization of Flowering Plants. 187 
brought directly into contact with the ovule. The observations 
of Darwin, extending over a period of thirty-seven years, proved 
that the best offspring is produced when the pollen of one flower 
is applied to the stigma of another flower, either of the same 
plant or of the same species. This is called cross-fertilization, 
and is the rule with the great majority of flowering plants. On 
the other hand, some plants are so modified as to ensure self- 
fertilization, as in the violets, where, in addition to the ordinary 
flowers, there are inconspicuous ones which do not open, but yet 
produce seed.* 
There are many contrivances for hindering or limiting self- 
fertilization on the one hand, and of facilitating cross-fertiliza- 
tion on the other; or, finally, in default of cross-fertilization, of 
ensuring ultimate self-fertilization. 
Plants may broadly be stated to be either wind-fertilized, which 
is generally the case in those with inconspicuous flowers, or the 
pollen is conveyed to other flowers by the agency of insects, 
which are attracted to them by their bright colours, size, per- 
fume, or by their secretion of honey. As an example of wind- 
fertilization may be cited the case of the conifers. Here the 
stamens and the ovules occur on different flowers, and frequently 
on different plants. The stamens are arranged as little spikes 
or cones formed of scales, the edges of which are slightly turned 
back, forming a depression or shallow trough in which the pollen 
from the stamen immediately above is deposited. When a gust 
of wind comes the pollen is dispersed in clouds of yellow dust,— 
sulphur rain as it has been called. Something similar occurs 
with the yew. Here the connectives of the anther-lobes terminate 
in a kind of shield with the anthers on the under surface, and, as 
several are joined together, they form roundish heads. When 
the weather is at all damp they lock closely together, but under 
the influence of a warm dry atmosphere the shields contract, 
allowing the pollen to make its way through the chinks when the 
branches are shaken by the wind. 
Very early in the spring, almost before winter has departed, it 
is a great pleasure to see once more the drooping catkins of the 
hazel, and ona closer search the beautiful crimson stigmas of the 
female flower will be discovered. When the pollen is ripe it is 
blown away in clouds, some of it falling upon a neighbouring 
stigma, and when all the pollen is shed the catkin falls off. 
Most of our forest-trees, such as the oak, beech, ash, chest- 
nut, elm, and walnut, are fertilized in this way, and in these 
cases the flowers come to maturity before the leaves are fully 
developed. 
* These generally grow in situations where insects are scarce, as in damp 
woods, &e. 
