The regulation of light

1129. The regulation of light is the remaining point. Light sometimes requires to be excluded, sometimes to be modified, and sometimes to be increased, in order to improve the qualities of vegetables; and hence the origin of thinning the leaves which overshadow fruits and flowers, the shading of cuttings, seeds, &c., and the practice of blanching. The latter practice is derived from accidents observable among vegetables in a wild state, and its influence on their quality is physiologically accounted for by the obstruction of perspiration, and the prevention of the chemical changes effected by light on the epidermis.