Facts, very numerous and varied, united to warrant us in concluding that gamogenesis commences where the forces which conduce to growth are nearly equilibrated by the forces which resist growth (§ 78); and the induction that in plants, fertilized germs are produced at places where there is an approach towards this balance, we found to be in harmony with the deduction that an advantage to the species must be gained by sending off migrating progeny from points where nutrition is failing. Other things equal, failure of nutrition may be expected in parts which have the most remote or most indirect access to the materials furnished by the roots--materials which have to be carried great distances by a very imperfect apparatus. The ends of lateral axes are therefore the probable points of fructification, in aggregates of the third order that have taken to growing vertically. But if these points at which nutrition is failing, are also the points at which the colours inherited from lower types are likely to recur in more marked degrees than elsewhere; then we may infer that the organs of fructification will not unfrequently co-exist with such colours at the ends of such axes. How may the resulting contrast between the older fronds and the fronds next the germ-producing organs be increased? If uninterfered with it would be likely to diminish. These traits inherited from remote ancestry might be expected slowly to fade away. How, then, is the intensification of them to be explained? If a contrast of the kind described favours the propagation of a race in which it exists, it will be maintained and increased; and if we take into account an agency of which Mr. Darwin has shown the great importance--the agency of insects--we shall have little difficulty in understanding how such a contrast may facilitate propagation. We cannot, of course, here assume the agency of insects so specialized in their habits as Bees and Butterflies; for their specialized habits imply the pre-existence of the contrast to be explained. But there is an insect-agency of a more general kind which may be fairly counted upon as coming into action. Various small Flies and Beetles wander over the surfaces of plants in search of food. It is a legitimate assumption that they will frequent most those parts in which they find most food, or food most to their liking--especially if at the same time they gain the advantage of concealment. Now the ends of axes, formed of young, soft, and closely-packed folia, are the parts which more than any others offer these several advantages. They afford shelter from enemies; they frequently contain exuded juices; and when they do not, their tissues are so tender as to be easily pierced in search of the sap. If, then, from the first, as at present, these ends of axes have been favourite haunts of small insects; and if, where the closely-clustered folia contained the generative organs, the insects