In general it is to be said that stamens and pistils may reach functional maturity in darkness or diffuse light, and if pollination is provided for, seed and fruit formation may ensue. The diminution of light has the effect of transforming inflorescences into leafy shoots in some instances, however. The more common reaction consists of alterations in the size, form, and color of the perianth, and greater changes are induced in the petals than in the sepals. The corolla shows greater decrease in size in _Melandryum_ and _Silene_, in diffuse light, though the relative form is maintained. The writer has obtained most striking results from growing flowers of _Salvia_ (sage) in a dark chamber, inclosing the inflorescence only. In the normal flower the irregular scarlet corolla attains three times the length of the calyx, and two stamens extrude from under the upper lip. When grown in darkness, the corolla with the adherent stamens measure about three millimetres in length, or one twelfth the normal, and are scarcely more than half the size of the calyx, which is but two thirds the size of similar organs grown in the light. The color is entirely lacking from the corolla, and is found only along the veins of the calyx. In other instances in which the corolla is composed of separate members, an unequal reaction is exhibited. The corolla of nasturtium (_Tropæolum majus_) consists of five approximately equal petals. Flowers of this species grown in darkness show one of nearly normal stature, two of reduced size, while the remaining two take the form of club-shaped bracts. The diminished size of the perianth of cleistogamous flowers of such types as the violet is due directly to the action of diminished light upon the hidden or inclosed flower. The influence of light upon the structure, reproductive processes, and distribution of the lower forms brings about the most widely divergent reactions, which can not be described here. The distribution and color of marine algæ depend upon the depth of the water and the consequent intensity of the light. This gives rise to distinct zones of aquatic vegetation. Thus in one series of surveys the _littoral_ zone, the beach area covered at high water and exposed at low water, was found to furnish proper conditions for green, brown, and red algæ. The _sublittoral_ zone, extending to a depth of forty metres, is furnished with red algæ, increasing in number with the depth, and the brown algæ disappear; while the _elittoral_ zone, from forty to one hundred and ten metres, is inhabited by red algæ alone. The number of species of vegetal organisms below this depth is extremely small. An alga (_Halosphæria viridis_) has been brought up from depths of one thousand to two thousand metres.