6o 
POLLINATION 
between gain and loss may be affected in many ways, owing 
to the exceedingly delicate adjustment of the inter-relation- 
ships of the life of plants and animals in any district. 
Darwin’s example of the effect of cats upon clover ( Origin 
of Species, p. 57) illustrates this. The introduction of 
cultivation and therefore of new forms of plants into a 
district may produce serious effects upon the general 
balance of life there, even in the parts of the district most 
removed from the cultivated area ; e.g. a field of clover may 
draw off most of the bees from the wild flowers. 
Some plants can risk more for cross-pollination than 
others ; e.g. an annual plant must set seed well, and so we 
find most annuals fully capable of autogamy. Long-lived 
perennials on the other hand can afford to try mainly for 
cross-pollination, and may even become incapable of auto- 
gamy altogether. The factors which have produced the 
particular phenomena seen in the pollination of any given 
flower are very numerous, and the problem to be solved 
before we can fully explain the phenomena is of a most 
complex description. Account has to be taken of vegeta- 
tive reproduction, amount of storage of material carried on 
by the plant, climate, competition with other plants and so 
on. On comparing the floral phenomena of the same plant 
in different countries, we find a remarkable amount of 
variety, and this is no doubt largely correlated with the 
variety in the general conditions of life, &c. In this 
connection it is of great interest to study the floral mechan- 
isms and insect visitors of the different species of such 
genera as Epilobium, Phacelia, Geranium, Gentiana (see 
Pt. II. and Muller’s Fertilisation of Flowers) or such families 
as Caryophyllaceae, where within a small circle of related 
forms every stage may be seen, from high types with 
complex mechanisms and cross-pollination down to low 
types with simple mechanisms and self-pollination. 
The earliest flowers must have depended upon the wind 
for pollen transport, and were therefore anemophilous or 
wind fertilised (better wmd-pollmated). This mode of polli- 
nation is not economical ; vast quantities of pollen must be 
produced to ensure that some shall reach the ovules. 
Comparatively few flowering plants retain the anemophilous 
condition of their ancestry, and these have mostly acquired 
