X 
distinct flowers, then termed unisexual. They are either upon the 
same plant, or monoecious , or upon different plants, when they are 
styled dioecious. 
The manner in which the fertilization of the ovules takes place 
is still involved in much obscurity. It is, however, certain that the 
contact of the pollen with the stigma is necessary for its accom¬ 
plishment; and this end is attained by Nature in various ways. In 
some instances the filaments of the stamens are endowed with a 
peculiar irritability, which causes them, when touched by insects or 
otherwise, to bend towards the stigma and discharge the contents 
of the anthers; this is the case with the flowers of the Barberry. 
In the Stinging Nettle the filaments are curved spirally within the 
calyx, and, when the latter expands, spring up suddenly and scatter 
the fertilizing grains over the adjacent pistils. In many plants the 
elastic coat of the anther itself performs a similar office, and the 
liberated pollen floats in clouds and becomes deposited upon the 
Jtigmas; in Pine woods, during the flowering season, the air is 
frequently filled with the minute yellow grains of pollen thus dis¬ 
charged. That of monoecious and dioecious plants is often con¬ 
veyed to the pistils by the bees and flies attracted by the honey in 
the flowers, and whose bodies are usually furnished with hairs, to 
which the grains readily adhere. The pollen-grains, however, con¬ 
veyed to the stigma, are retained upon that organ by means of a 
viscid fluid secreted upon its surface, and, after remaining there a 
short time, send forth tubes, which, piercing the substance of the 
pistil and penetrating into the ovary, impregnate the ovules therein 
contained. 
The numerous hybrids of some flowers so abundantly raised by 
the florist are produced by the contact of the pollen with the 
stigmas of distinct species of the same genus. Similar varieties 
are not uncommon in Nature; but they rarely produce seed, and 
consequently these abnormal forms seldom become permanent. 
The ovary, when matured, becomes the fruit of the plant, and 
