_Vivipary_ is a particular case of proliferation, in a certain sense, where the seeds appear to germinate _in situ_, and we have small plants springing from the flowers, reminding us of wheat which has sprouted in the shocks in damp weather. In reality, however, the grains are here replaced by bulbils which sprout before they separate from the inflorescence. In varieties of _Poa_, _Polygonum_, _Allium_, _Gagea_, etc., this phenomenon is constant in plants growing in damp situations. _Prolepsis._--It frequently happens that branches or whole plants are suddenly defoliated in summer,--_e.g._ by caterpillars or other insects--at a time when considerable stores of reserves had already been accumulated during the period of active assimilation. In such cases the axillary buds, which would normally have passed into a dormant condition over the winter had the leaves lived till the autumn-fall, suddenly shoot out into _proleptic_ shoots (also termed Lammas shoots), and reclothe the tree with foliage. The wood of the year in which this occurs may exhibit a double annual ring, and the vigour of the tree is likely to suffer in the following season and no fruit be matured. Proleptic branches may also be due to the shooting out of accessory buds--_i.e._ extra buds found in or near the leaf-axils of many plants, such as Willow, Maples, _Cercis_, _Robinia_, _Syringa_, _Aristolochia_, etc.--which do not normally come to anything, or do so only if a surplus of food materials is provided. _Dormant buds_, or _preventitious buds_, are such as receive no sufficient supply of water and food materials to enable them to open with the other buds in ordinary years, for in most trees only the upper buds on the branches develop into new shoots. The lower buds do not die, however, but merely keep pace with the growth in thickness of the parent branch, and may be elongated sufficiently each year to raise the minute tips level with the bark, their proper cambium only remaining alive but not thickening the bud. When, by the breaking of the branch above the insertion of the dormant bud--or by pruning, defoliation by insects, etc.--the transpiration current and supplies of food materials are in any way deflected to the minute cambium and growing points of the dormant buds, they are stimulated to normal growth, and may grow out as _epicormic shoots_ or "shoots from the old wood." In many cases such epicormic shoots are stimulated to grow out by suddenly exposing an old tree to more favourable conditions of root-action and assimilatory activity, owing to the felling of competing trees which previously hemmed it in from light and air, and restricted the spread and action of its roots in the soil. This is often seen in old Elms, Limes, etc. It is by such means as the above that substitution branches are obtained when a leader is broken or cut away.