CHE REFERENCE LIBRARY - ZetaTalk

116 TIIE NURSERY-MA NiJALing of uncongenial kinds are surely to be avoided, but it is nowtoo late to raise the question in the abstract.Grafting is not unknown in nature. Often limbs of treesgrow together solidly when they cross. Fig. 129 (left) shows anatural graft Of two trunks which in some way became en:tangled. Fig. l2C3 (right) is a similar case, but here the fourtrunks were tied together intentionally and are now growninto a firm union. In these cases the trees are of the samekind or species.The limit within which graftage is possible or desirablebetween species, is determined only by experience. Probablyall exogenous plants __ those with a distinct bark and pith -can be regularly grrlf ted. Plants must be more or less closelyrelated to allow of successful graftage of the one on the other.AS a rule, plants of close botanical relationship, especially thoseof the same genus, intergraft with more or less ease ; yet thisrelationship is by no means a safe guide, particularly as thecurrent fashion among taxonomists of splitting up genera intofragments obscures nffinities. A plant will often thrive betteron a species reputed to be of another genus than on a congener.The pear, for example, does better on many thorns than onthe apple. Sonietirnes plants of very distinct genera uniterea.dily. Thus :~mong caclt i, the leafless zygocactus (usuallyknown as epiph~~lluni) grows well on the leaf-bearing pereskia.It should be borne in mind that union of tissues isnot a proof of affinity. Real affinity can be measured onlyby the thrift, healthfuhless and loilgevity of the cion.The bean has been known to make a union with the chrysanthemum,but it almost immediately died. Soft, tissues, inparticular, often combine in plants that possess no affinitywhatever, as we commonly understand the term. Keitherdoes affinity refer to relative sizes or rat,es of growth of stockand cion, although the term is sometimes used in this sense.It cannot be said that some varieties of pear lack affinity for