[Illustration: Fig. 48. Control ecad of _Ranunculus sceleratus_, holard 40% (200 cc.).] In sunny habitats, the light intensity is most easily reduced by means of cloth awnings, which can be put in place conveniently. It is not a difficult matter to produce effective shade by using shrubs or small trees for this purpose. This plan is especially advantageous in habitats too remote to make frequent visits feasible. When a shrub or tree is used, the experiment necessarily requires a longer time, though this disadvantage is partly compensated by the fact that the shelter requires practically no attention after the shrub is once established. Forest plantations furnish excellent examples of this kind of experiment. On the other hand, clearings afford the only examples of habitats modified in such manner as to increase the light. In nature, the diffuse light in which shade plants grow is due to the presence of tall plants, chiefly shrubs and trees, and an increase in the light intensity is possible only through the thinning-out or removal of the plant screen. This is a task of considerable magnitude in forests, but it can be readily accomplished in thickets and at the edges of woodlands. It is quite practicable to establish a series of awnings or clearings of various light values, but the labor required is hardly worth while when it is recalled that the method of transfer makes it possible to take advantage of the various intensities already found in nature. METHOD OF CONTROL CULTURES