MESSMATES, MUTUALISTS, AND PARASITES 85 
number of small bodies known as Ovules, destined to become 
seeds, and the most important part of an ovule is a minute egg- 
cell or ovum. On the top of the pistil is a rough and ae 
surface, the Stigma. 
Pollination is a necessary preliminary to fertilization, aaa 
consists of the transfer of ripe pollen-grains to the stigma. 
Supposing this to have been effected, a thread-like pollen-tube 
grows from each grain into the cavity of the carpel until it reaches 
that part of the ovule where the egg-cell is located. A nucleus- 
containing fragment of protoplasm (equivalent to a sperm) from 
the tip of the tube is then transferred to this cell, with which it 
fuses. The egg-cell, thus fertilized, develops into an embryo, and 
the rest of the ovule undergoes certain modifications, the total 
product being a seed. 
A stigma may be pollinated by grains developed in the stamens 
of its own flower (self-pollination), or by grains derived from other 
flowers (cross-pollination). The latter, since it is followed by 
cross-fertilization, is the more desirable event, and the actual 
transfer of pollen from flower to flower is effected by water, 
wind, or animals, according to the nature of the arrangements 
which have been evolved. We are here only concerned with 
animal-pollinated (zoophilous) flowers, and in the large majority 
of these the agents are insects. Many of the characters of insect- 
pollinated (entomophilous) flowers have been evolved with re- 
ference to the attraction and reception of suitable guests. It was 
at one time the general belief that the varied odours and hues of 
flowers came into existence simply and solely for the delectation 
of mankind; as a matter of fact their significance is utilitarian, and 
has reference to the needs of plants themselves. For scent and 
colour are the means employed to attract insects (and sometimes 
other animals) capable of doing the work of cross-pollination. 
It is fortunate that the odours generally commend themselves 
to us, but this is not always so, for certain flowers (e.g. some 
Arums) smell like carrion, the object being to attract those flies 
which revel in putridity. As to colour there is of course a great 
variety, and some tints appeal to special visitors. Typical “bee 
flowers”, for example, are commonly reddish-purple, purple, or 
blue. Other forms depend upon dusk-loving insects, especially 
moths, for their cross-pollination, and these are white or pale in 
hue, which gives them the best chance of being seen (fig. 1079). 
