FLOWER-GARDENING. 157 



that the latter are not liable to suffer bj evaporation, because 

 of their communication with the parent plant. 



326. As cuttings strike roots into the earth by the action of 

 leaves or leaf-buds, it might be supposed that they will strike 

 most readily when the leaves or leaf-buds are in their greatest 

 vigor. 



327. Nevertheless, this power is controlled so much by the 

 peculiar vital powers of different species, and by secondary 

 considerations, that it is impossible to say that this is an 

 absolute rule. 



328. Thus Dahlias and other herbaceous plants will strike 

 root freely when cuttings are very young ; and Heaths, Aza- 

 leas, and other hard-wooded plants, only when the wood has 

 just begun to harden. 



329. The former is, probably, owing to some specific vital 

 excitability, the force of which we cannot appreciate ; the lat- 

 ter either to a kind of torpor, which seems to seize such plants 

 when the tissue is once emptied of fluid, or to a natural slow- 

 ness to send downwards woody matter, whether for wood or 

 not, which is the real cause of their wood being harder. 



330. If ripened cuttings are upon the whole the most fitted 

 for multiplication, it is because their tissue is less absorbed 

 than when younger, and that they are less likely to suffer 

 either from repletion or evaporation. 



331. For, to gorge tissue with food, before leaves are in 

 action to decompose and assimilate it, is as prejudicial as to 

 empty tissue by the action of leaves, before spongioles are pre- 

 pared to replenish it. 



332. For this reason, pure silex, in which no stimulating 

 substances are contained (silver sand), is the best adapted for 

 promoting the rooting of cuttings that strike with difficulty. 



333. And for the same reason, cuttings with what garden- 

 ers call a heel to them, or a piece of the older wood, strike 

 root more readily than such as are not so protected. The 

 greater age of the tissue of the heel renders it less absorbent 

 than tissue that is altogether newly formed. 



