*218 PEIKCIPLES OF GARDENING. [CH. VII. 



is produced by training a branch in a waving form, 

 for two thirds of its length are placed horizontally as 

 in the accompanying outline. Other modes of inter- 

 rupting the rapid flow of the sap by checking its 

 return has been noticed in a previous chapter. 

 Among which modes are ligatures and wounds round 

 the bark. 



Light and heat are so combmed, and so equally 

 essential for the ripening of fniit, that they may be 

 considered conjointly. They are both diminished in 

 ungenial summers, and in such, finiit ripens indiffer- 

 ently, or not at all, being, if it does ripen, deficient in 

 colour, as well as flavour. In our latitudes, however, 

 warmth is more deficient than light for the matui'ing 

 of exotic plants — therefore, by securing to them a 

 higher temperature, we have the peach, the melon, 

 the mango, and the pine-apple as richly flavom-ed, 

 and even superior to the excellence they attain in 

 their native climes. 



It must be remembered, in considering this branch 

 of our subject, that all cooling is occasioned either by 

 the heat being conducted from a body by a colder, which 

 is in contact with it, or by radiating from the body 

 cooled, though circumstances accelerate or retard the 

 radiation, and whatever checks the radiation of heat 

 from a body keeps it warmer. For example, — a ther- 

 mometer placed upon a grass-plat, exposed to a clear 

 sky, fell to 35°, but another thermometer witlun a 



