OP TRAINING. 259 



early flowers to perish from cold. That a blackened 

 surface does produce a beneficial effect upon trees 

 trained over it, is, however, probable, although not in 

 insuring the maturation of fruit ; it is by raising 

 the temperature of the wall in autumn when the 

 leaves are falling, and the darkened surface becomes 

 uncovered, that the advantages are perceived by a 

 better completion of the process of growth, the result 

 of which is ripening the wood. This is, indeed, the 

 view taken of it by Mr. Harrison, who found the 

 practice necessary, in order to obtain crops of pears 

 in late seasons at Wortley in Yorkshire (see Sort 

 Trans., iii. 330; and vi. 453.) It hardly need be 

 added that the effect of blackening will be in propor- 

 tion to the thinness of the training, and vice versd. 



Another object of training is, to place a tree in such 

 a state of constraint that its juices are unable to cir- 

 culate freely, the result of which is exactly that 

 already assigned to the process of ringing (see p. 

 254). If a stem is trained erect, it will be more 

 vigorous than if placed in any other position, and its 

 tendency to bear leaves rather than flowers will be 

 increased ; in proportion, as it deviates from the per- 

 pendicular is its vigour diminished. For instance, if 

 a stem is headed back, and only two opposite buds 

 are allowed to grow, they will continue to push 

 equally, so long as their relation to the perpendicular 

 is the same ; but, if one is bent towards a horizontal 

 direction, and the other allowed to remain, the growth 

 of the former will be immediately checked ; if the 

 depression is increased, the weakness of the branch 



