The vitality in the branches of most of the species is very great, the smallest piece, as a rule, emitting roots and developing into a plant in a comparatively short time.  The branches are soft, and easily broken, so that, in gathering the fruits, many pieces are broken off and cast aside; these soon grow into plants, and in a short time an extensive “colony” of Opuntias springs up where previously only one had been.  The seeds, too, are a ready means of increase, being distributed by birds and other animals, which eat the fruits.  In consequence of this free vegetative character, the Opuntias introduced into some of our colonies have become a pest almost as difficult to deal with as the rabbit scourge in Australia.  In English gardens, however, there is no danger of Opuntias getting the upper hand.  The adaptability of the majority of the kinds for cultivation under what may be termed adverse conditions for other plants, and the ease with which they may be propagated, render the management of a collection of these plants an easy matter.  Amongst other Cactuses, Opuntias have a striking effect, and a selection of them should be grown in even the smallest collections.  A few of them may be recommended specially as attractive plants for a sheltered, sunny rockery.

Cultivation.—­The cultural requirements of the Opuntias may more conveniently be referred to under the description of each kind.

Propagation.—­This entails no exceptional treatment; the numerous seeds contained in each fruit germinate freely if sown in sandy soil, and placed on a shelf in a warm house; and the smallest branches root quickly if planted in pots of open soil and kept in the Cactus-house.  Large branches root just as freely as small ones.  At Kew an enormous specimen, which had grown tall, and developed a thicket of branches too great for the house where it grew, was reduced most summarily by simply cutting off the head of branches and planting it in the ground where the original specimen had been.  In a short time this “cutting” was well rooted, and made better growth than it had before the operation was performed.

As stocks for grafting, many of the more robust kinds of Opuntia are well adapted, and very singular-looking specimens may be obtained by making the most of this fact.  One of the crested or monstrous forms, when grafted on a flat-stemmed kind, presents the queerest of appearances, looking like a large green cockscomb growing out of the top of a bladdery kind of stem.  Equally odd combinations may be made by grafting a flat-stemmed kind on one whose stem is cylindrical.  As all the kinds unite with the greatest ease, a taste for oddities among plants may easily be gratified by making use of Opuntias in this way.  The time most favourable for the operation is spring-say, the month of April.  For full information on how to graft Cactuses, see Chapter IV., on Propagation.

Species.