244 PROPAGATION BY GRAFTING, ETC. 



account of the physiological differences which may and do frequently 

 exist. 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. 



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 

 hypertrophy, as the other did from atrophy. The analogy of con- 

 sistence 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 Acer platanoides the only species of Acer 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. 



The modifications effected by the graft form 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 sometimes altered by grafting. Thus 

 Acer eriocarpum, when grafted on the common sycamore, attains in 

 Europe double the height which it does when raised from seed. 

 Cerasus canadensis, which in a state of nature is a rambling shrub, 

 assumes the habit of an upright shrub when grafted on the common 

 plum. Various species of Cytisus become greatly invigorated when 



