INTRODUCTION. LEA VES. i ? 



produced, and just in proportion to their defectiveness will the tree, bush, or vine bo 

 deprived of health and fruit-producing power. 



Intimately connected with the leaves is the movement of the sap in trees, and of this 

 the cultivator should not be entirely without knowledge. Sap moves under the impulse 

 of heat, which changes it from a more or less thickened and sluggish to a fluid and active 

 state. It passes upwards from cell to cell through every part of the tree, but chiefly 

 through the new outer tissue, and the greater the force of its propulsion, and the fewer 

 the channels to which it may be confined, the more luxuriant is the growth or formation 

 of new parts. A familiar example of this is seen in the pollarding or cutting down of 

 willows, and the long strong shoots resulting. It is the same with respect to fruit trees, 

 and, as a rule, the closer or more severe the pruning to which they are subjected the 

 stronger and, for a time, the less fruitful are the shoots that follow. From this it will be 

 apparent that more harm than good may be done by the knife, if it is applied in ignorance 

 of the conditions that affect the movement of sap. If its flow from the roots through the 

 stem is divided into ten thousand channels, as represented in as many branchlets or 

 twigs, its force through each is weakened, and so of necessity is the growth of 

 those parts, whereas if the sap is contracted or confined to a few channels, as the 

 result of cutting out some and shortening other branches, so is the sap force increased 

 and in the same proportion is the growth that follows. An analogy is found in forcing 

 water through a syringe : the smaller and more numerous the perforations, the finer, hence 

 weaker, the spray or much-divided stream. The sap of trees, crude when it commences 

 its upward course, passes from the stems to the leaves, and is there changed, by 

 exposure to the sun and the action of light and air ; it afterwards commences its 

 downward course beneath the bark, depositing starchy and gummy matter on the 

 way, thickening the stems and providing nourishment for the buds that are formed 

 for the production of flowers and successive growths of stems and leaves. Sap then 

 until it reaches the leaves is impure ; after passing through those that are healthy and 

 exposed to the sun, or fullest possible light, it descends purified and fulfils its vital 

 mission. The downward course of the sap is clearly seen, if a narrow strip of bark is 

 removed quite round a stem when in full leaf, for the part above the stem will thicken 

 by the deposition of matter in the descending sap. From this fact arose the old plan 

 known as "ringing " or holding up the sap, so to say, for enlarging the fruit above the 

 part from which the bark is removed. Another method for effecting the same object is 

 securing wire ligatures round the stems ; this was known to the ancients, and one of the 



YOL, I, D 



