It has already been hinted that the wonderful variety of form and colour exhibited by flowers has some connexion with this important matter of the transfer of pollen, and the reader who is really interested in the investigation of the significance of this great diversity will find it a most charming study to search into the advantages (to the flower) of the different peculiarities presented, especially if he endeavours to confirm his conclusions by direct observations of the methods by which the pollen cells are distributed to the stigmas. Pollen cells are usually distributed either by the agency of the wind or by insects; and it is generally easy to determine, by the nature of the flower itself, which is the method peculiar to its species. A wind-pollinated flower is generally very inconspicuous. It produces no nectar, which forms the food of such a large number of insects, and has no gaudy perianth, nor does it emit any odour such as would be likely to attract these winged creatures. Its anthers generally shed an abundance of pollen, to compensate for the enormous loss naturally entailed in the wasteful process of wind-distribution, and the pollen is so loosely attached that it is carried away by the lightest breeze. Further, the anthers are never protected from the wind, but protrude well out of the flower; and the stigma or stigmas, which are also exposed, have a comparatively large area of sticky surface, and are often hairy or plumed in such a manner that they form effectual traps for the capture of the floating pollen cells. An insect-pollinated flower, on the other hand, has glands (_nectaries_) for the production of nectar, and its perianth is usually of such a conspicuous nature that it serves as a signal to attract the insects to the feast. (In some instances the individual flowers are very small, but these are generally produced in such clusters that they become conspicuous through their number.) Often it emits a scent which assists in guiding the insects to their food. Its stamens are generally so well protected by the perianth that the pollen is not likely to be removed except by the insects that enter the flower; and the supply of pollen is usually not so abundant as in the wind-pollinated species, for the insects, travelling direct from flower to flower, convey the cells with greater economy. The stigmas, too, are generally smaller, and are situated in such a position that, when mature, they are rubbed by that portion of the insect's body which is already dusted with pollen.