is consequent solely, or even chiefly, on the differential actions experienced by the individual plant. Though there is good reason to believe that the rate of growth in each part of each leaf is affected by the incidence of light, yet contrasts so marked and so systematic as these are not explicable without taking into account the inheritance of modifications either functionally caused or caused by spontaneous variation. Clearly, the tendency will be towards the preservation of a plant which distributes its chlorophyll in the most advantageous way; and hence there will always be a gravitation towards a form in which shaded parts of leaves are undeveloped. § 229. From compound leaves to simple ones, we find transitions in leaves of which the divisions are partial instead of total; and in these we see, with equal clearness, the relations between forms and positions that have been traced thus far. Fig. 213 is the leaf of a Winter-aconite in which, round a vertical petiole, there is a radial distribution of half-separated leaflets. The _Cecropia_-leaf, Fig. 214, shows us a two-sided development of the parts beginning to modify, but not obliterating, the all-sided arrangement; and this mixed symmetry occurs under conditions that are intermediate. A more marked degree of the same relation is presented in the leaf of the Lady’s Mantle, Fig. 215. And then in the Sycamore and the Vine, we have a cleft type of leaf in which a decided bilateralness of form co-exists with a decided bilateralness of conditions. [Illustration: Figs. 213–215.] [Illustration: Figs. 216–218.]