LECTURES. 35 
to the ground with the last petal, only to make a futile attack on 
another flower. 
In Composite we have a family in which there is a combination of 
all the characteristics most favourable to cross-fertilisation by small 
insects and bees alike, viz. (1) the close association of many flowers in 
heads ; (2) the accessibility of the honey, as well as its abundance, and 
its protection from rain ; (3) a pollen mechanism. At the same time 
most of the species are adapted for self-fertilisation when insect visits 
fail. ‘These facts account for the great abundance of genera and spe- 
cies in the order. For the sake of non-botanists I may mention that 
each little tube of the head (e.g. in the Daisy) constitutes a perfect 
flower. The anthers cohere to form a hollow cylinder, and dehisce 
inwards, filling this cylinder with pollen, before the flower opens. The 
style is furnished with a brush of hairs, which forces out the pollen 
gradually, so that an insect crawling over the head is dusted with pol- 
len underneath. When the style has forced all the pollen out, it 
splits down the centre exposing the stigmatic surfaces. If insect visits 
have been few, some pollen will be still adhering to the style, and will 
cause self-fertilisation ; whereas if they are plentiful, an insect coming 
from a younger flower will effect cross-fertilisation. Further, the de- 
velopment of the florets progresses from the margin towards the centre, 
so an insect alighting on the outer ray will touch the oldest (.¢. the 
female) part first. And here we may notice a little piece of economy 
on the part of Nature. The pollen on the vuter florets would 
generally be shed before any stigmas were ripe, and would be wasted, 
so it is entirely dispensed with ; and not only this but the brush ap- 
paratus on the style of these outer florets is wanting in many species. 
The honey is secreted at the bottom of the corolla tube, which is often 10 
or 12 m.m. long, but the tube is so narrow at the bottom that the honey 
rises into the broader throat, where it is accessible to short-lipped insects. 
This causes no injury, as it would in the case of flowers specialised for 
bees, for an insect effects cross-fertilisation by simply crawling over the 
flower, and no intelligence is required for this. We may also notice 
that the Composite have light seeds in which the calyx has become 
specialised into a sort of parachute, which enables them continually 
to change their ground. In Carduus Arvensis, the commonest of our} 
thistles, the brush apparatus is still more complete. It is terminated 
by a ring of longer hairs, and ‘the pollen grains are sticky enough tc 
adhere to it. The style then grows out several m.m. beyond the c 
rolla tube, and if sufficient insects come (which will always be the cas 
in fine weather), the pollen is soon removed. The style then open 
