THE FLOWER 
67 
accessory organs , or non-spore-bearing leaves, forming a 
perianth , which is most often in two series, the outer leaves 
( sepals ) forming a protective calyx, the inner {petals) a 
coloured corolla. 
We shall deal with the morphology from a phylogenetic 
and ecological point of view, endeavouring to trace the 
gradual evolution and differentiation of the various parts 
in the light of the principle of the physiological division of 
labour. It is necessary to keep clearly in mind what has 
been said above about cross- and self-fertilisation and polli- 
nation. The primary object of the flower, to speak in 
a figurative manner, is to set seed with as much economy 
as possible. A saving of material in the flower may be 
applied to increasing the weight or number of the seeds. 
A great number of plants are adapted chiefly to cross- 
pollination and this introduces numerous complications into 
their morphology. Others again have, in the course of ages, 
become adapted to self-fertilisation, but previous adaptations 
for crossing may still remain in a more or less imperfect 
condition. Other important points are protection of the 
essential organs from the weather, economy of pollen and 
ovules, improvement of mechanisms for pollination, attrac- 
tion of more and cleverer insects, exclusion of less desirable 
insects, and so on. All of these specialisations are reflected 
in floral morphology. 
It is not altogether improbable that at a very early 
period the ancestors of the present flowering plants had 
simple cone-like flowers, each composed of an axis bearing 
micro- and mega-sporophylls. Such a flower is approxi- 
mately represented by the cone of Selaginella, and by 
comparing with it the flowers of to-day in all their variety 
we can trace the corresponding organs throughout, and infer 
what new organs have arisen and what changes have oc- 
curred. Comparative study of floral structure shows that 
the seeming infinite variety can be largely brought under 
a few heads which apparently represent lines upon which 
evolution has progressed in connection with the specialis- 
ations outlined above. With these features we shall now 
deal in order, and afterwards with the special morphology 
of the floral organs, and their natural history. 
Descriptive Terms and further details are given after 
5 -2 
