Double Flowers
Generally speaking, the epithet Double is applied to flowers of very varied structural conformation. The most common conditions rendering a flower Double, in the popular acceptation of the term, are substitutions of petals or petal-like bodies for stamens and pistils, one or both. Another very common mode of Doubling is brought about by a real or apparent augmentation in the number of petals, as by multiplication, fission, &c. Double Flowers are often of much more value, from a purely horticultural standpoint, than single ones. The protective floral organs--the calyx and corolla--frequently wither quickly after fertilisation has taken place, whilst in those flowers in which the organs of reproduction have been metamorphosed into petaloid bodies, they remain, as a rule, in full beauty a much longer time. The predisposing causes of Doubling seem very different in various plants. In some, it may be brought about by an excess of nutrition; in others, by a process akin to starvation. In some cases, as in the common Kerria japonica, for example, there is a natural tendency for the flowers to become Double under cultivation. Single-flowered plants have been imported which, in a few years, have altogether ceased to produce single flowers. For a very exhaustive account of the various kinds of Doubling, and their morphological significance, the reader is referred to one of the Ray Society's publications, "Vegetable Teratology," by Dr. M. T. Masters. The means adopted by some successful growers to obtain Double Stocks will be described under Stocks.