Thus, if anthocyanin is present, together with a small amount of acid, the leaves are turned violet, as in the case of the autumn leaves of the Dogwood and the Spindle Tree; or purple, like those of the Service Tree. A larger proportion of acid produces, with the anthocyanin, the brownish green tint of the Alder leaves; or the brownish yellow of the Oak; while still larger proportions will turn the anthocyanin yellow, orange, red, or scarlet, according to the quantity in which the latter is present. Thus we can account for the rich yellow of the Maple in autumn, the orange of the Aspen leaves, the beautiful scarlet tints of the Mountain Ash and the Barberry, and the grand display of varied colours exhibited by the autumn Beeches. Again, before the leaves are shed, the buds that are destined to produce the new branches of the following spring are already formed. These may be seen on all deciduous trees and shrubs, some of them in the axils of the leaves, and others at the tips of the present twigs. Each bud is the embryo branch of the following year. Some of them are destined to produce leafy branches only; some are to develop into branches bearing both floral leaves and flowers; while others are to produce flowers without floral leaves; and it is interesting to note that, even at this stage, sections of the buds, examined with the aid of a microscope, will reveal the future leaves and flowers compactly concealed within their scaly, protective coverings. In October we may see the well-formed catkins of the Birch that are to bloom in the following April, in company with the ripe fruiting catkins of the present year. The Alder also bears its catkins that are to flower five months later, together with the woody remains of the female catkins of the previous spring; and the Hazel may be seen with its ripe nuts and its future flowers both on the same twig. [Illustration: THE ALDER IN AUTUMN, WITH THE CATKINS WHICH MATURE IN THE FOLLOWING SPRING.] The leaves, having manufactured the materials necessary for the formation of the buds that are to produce the leaves and flowers of the following year, and then transferred their remaining store of nutrient matter to a suitable storehouse for the winter, are now practically empty and lifeless. Had they remained alive and active, they would have endangered the life of the tree by giving off more moisture than could be replaced by the inactive roots. In their present, lifeless condition they are useless to the tree; but by falling to the ground, and decomposing where they lie, they improve the soil by the addition of organic matter as well as of the mineral salts they contained.