INTRODUCTION. XV 



pede both the ascent and the descent of the fluids in a 

 gradual but certain manner. The tissue of which 

 branches are composed is certainly permeable to fluids 

 in every direction ; and there can be no doubt that the 

 vital action of the vessels of a plant is performed both 

 in the natural and in an inverted position. So long as 

 that erect direction of the branches which is natural to 

 them is exactly maintained, the flow of their fluids, 

 being subject to no interruptions, will take place in the 

 freest possible manner ; but the moment this natural 

 direction is deviated from, the vessels become more or 

 less compressed, their action is impeded, and finally, 

 if the inversion is perfect, it becomes so slow that an 

 accumulation of the proper juices necessarily takes place 

 through every part of the system. 



One of the objects of training is to produce the same 

 effect. Branches are bent more or less from their 

 naturally erect position ; their motion, in consequence 

 of the action of winds upon them, which is known to 

 facilitate the movement of the fluids, is totally de- 

 stroyed ; and hence arises the accumulation of proper 

 juice which is necessary to their fertility. Nor is the 

 influence of the stock of an essentially different nature. 

 In proportion as the scion and the stock approach each 

 other closely in constitution, the less effect is produced 

 by the latter ; and, on the contrary, in proportion to the 

 constitutional difference between the stock and the scion, 

 is the effect of the former important. Thus, when Pears 

 are grafted or budded on the wild species, Apples upon 

 Crabs, Plums upon Plums, and Peaches upon Peaches 

 or Almonds, the scion is, in regard to fertility, exactly 

 in the same state as if it had not been grafted at all. 

 While, on the other hand, a great increase of fertility is 

 the result of grafting Pears upon Quinces, Peaches 

 upon Plums, Apples upon Whitethorn, and the like. 

 In these latter cases, the food absorbed from the earth 



