PROPAGATION BY GRAFTING. ETC. 



283 



watery or non-elaborated sap, which it does not return to the plant on which 

 it grows by the bark, as in the case of other grafts ; and hence, says De 

 Candolle, the necessity of plants in general having a natural analogy between 

 the scion and the stock, is founded on the descent of the sap by the bark, 

 while the mistletoe, which absorbs the watery sap and returns nothing, can 

 live on all exogens of which the ascending sap is of a watery consistence. 

 As a proof that plants of the same natural family may be grafted on one 

 another, De Candolle succeeded in grafting the lilac and the fringe tree on the 

 ash, the fringe tree on the lilac, the lilac on the phillyrea, and the olive on 

 the ash and the privet ; and though these grafts did not live a long time, 

 on account of the physiological differences of the species, yet their having 

 succeeded at all sufficiently proves the anatomical analogy of plants within 

 the same natural order. This analogy is greater between plants of the 

 same genus ; more so still between individuals of the same species, and most 

 so between branches of the same individual, 



642. Physiological analogy. In a physiological point of view, the epochs 

 of vegetation are the principal points to be attended to, and hence no plant 

 can be grafted on another which does not thrive in the same temperature. 

 Two plants in which the sap is not in motion cannot be successfully 

 united^ because it is only when cellular tissue is in a state in which it can 

 form accretions that a vital union can be formed, and a reciprocal 

 activity must exist both in the stock and scion. Hence evergreen trees 

 seldom succeed for any length of time when grafted on deciduous kinds. 

 The analogy of magnitude is also of some importance, for if a large 

 growing tree is grafted on one naturally of small stature, the graft, by 

 exhausting the stock, will ultimately deprive it of life ; and when a small 

 or weakly growing species is grafted on a large vigorous one, it receives too 

 much sap, and ultimately perishes from superfluity, as the other did from 

 insufficiency. The analogy of consistence also merits notice. Soft woods 

 do not associate well with hard woods, nor ligneous plants with such as are 

 herbaceous, nor annuals with perennials. An analogy in the nature of the 

 sap is also requisite, experience having proved that plants with a milky sap 

 will not unite for any length of time with plants the sap of which is watery. 

 Thus the ^ Ver ^latanoides — the only species of ^'cer which has milky sap 

 — will not graft with the others ; and numerous as are the species of tree 

 on which the mistletoe grows, it is never found on those which have a 

 milky sap. 



643. The modifications effected by the graft, is a subject of great practical 

 interest to the cultivator. The graft neither alters the species, nor the 

 varieties, but it has some influence on their magnitude and habits, and on 

 their flowers and fruit. The apple grafted on the paradise stock becomes 

 a dwarf, and on the crab stock, or a seedling apple, a middle-sized tree. The 

 size of the stock here seems to influence the size of the graft ; but in the 

 case of the mountain ash, which is said to grow more quickly when grafted 

 on the common thorn, than when on its own roots, the stock is naturally a 

 smaller plant than the tree grafted on it. The habit of the plant is some- 

 times altered by grafting. Thus A'cer eriocarpum, when grafted on the 

 common sj'-camore, attains in Europe double the height which it does when 

 raised from seed. C'^rasus canadensis, which in a state of nature is a ram- 

 bling shrub, assumes the habit of an upright shrub when grafted on the 

 common plum. Various species of Cytisus become greatly invigorated when 



