A kindred truth, having like implications, comes into view when we observe the relative sizes of leaves on the same branch, where their sizes differ. Fig. 205 represents a branch of a Horse-chestnut, taken from the lowermost fringe of the tree, where the light has been to a great extent intercepted from all but the most protruded parts. Beyond the fact that the leaves become by appropriate growths of their foot-stalks bilaterally distributed on this drooping branch, instead of being distributed symmetrically all round, as on one of the ascending shoots, we have here to note the fact that there is unequal development on the upper and lower sides. Each of the compound leaves acquires a foot-stalk and leaflets that are large in proportion to the supply of light; and hence, as we descend towards the bottom of the tree, the clusters of leaves display increasing contrasts. How marked these contrasts become will be seen on comparing _a_ and _b_, which form one pair of leaves that are normally equal, or _c_ and _d_, which form another pair normally equal. Let us not omit to note, while we have this case before us, the proof it affords that these differences of development are in a considerable degree determined by the different conditions of the parts after they have been unfolded. Though those inequalities of dimensions whence the differentiations of form result, may be in many cases largely due to the inequalities in the circumstances of the parts while in the bud (which are, however, representative of inequalities in ancestral circumstances); yet these are clearly not the sole causes of the unlikenesses which eventually arise. This bilateralness resulting from the unequal sizes of the leaves, must be considered as due to the differential actions that come into play after the leaves have assumed their typical structures.