70 CUTTINGS. 



evaporation, because of their communication 

 with the parent plant. 



As cuttings strike roots into the earth by the 

 action of leaves or leaf-buds, it might be sup- 

 posed that they will strike most readily when 

 the leaves or leaf-buds are in their greatest 

 vigor. 



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. 



Thus Dahlias and other herbaceous plants 

 will strike root freely when cuttings are very 

 young ; and Heaths, Azaleas, and other hard 

 wooded plants, only when the wood has just 

 begun to harden. 



The former is, probably, owing to some spe- 

 cific vital excitability, the force of which we 

 cannot appreciate ; the latter either to a kind 

 of torpor, which seems to seize such plants 

 when their tissue is once emptied of fluid, or to 

 a natural slowness to send downwards woody 

 matter, whether for wood or not, which is the 

 real cause of their wood being harder. 



If ripened cuttings are upon the whole the 

 most fitted for multiplication, it is because their 



