FLOWER-GARDENING. 153 



parts developed in light, as in tlie subterranean roots of Beet, 

 Carrots, etc. 



285. What is true of color is also true of flavor, wliicli 

 equally depends upon light for its existence ; because flavor is 

 produced by chemical alterations in the sap caused by exposure 

 to light (229). 



286. The same thing occurs in regard to nutritive matter, 

 which in like manner is formed by exposure of leaves to light. 

 Thus the Potato, when forced in dark houses, contains no more 

 amylaceous matter than previously existed in the original tuber , 

 but acquires it in abundance when placed in the light, and 

 deposits it in proportion as it is influenced by light and air. 

 Thus, also, if Peaches are grown in wooden houses, at a distance 

 from the light, they will form so little nutritive matter as to be 

 unable to support a crop of fruit, the greater part of which will 

 fall off. And for a similar reason, it is only the outside shoots 

 of standard fruit-trees that bear fruit. Considerations of this 

 kind form in part the basis of pruning and training. 



287. Light is the most powerful stimulus that can be em- 

 ployed to excite the vital actions of plants, and its energy is in 

 proportion to its intensity ; so that the direct rays of the sun 

 will produce much more powerful effects than the diffused light 

 of day. 



288. Hence, if buds that are very excitable are placed in a 

 diffused light, their excitability will be checked. 



289. And if buds that are very torpid are exposed to direct 

 light, they will be stimulated into action. 



290. So that what parts of the tree shall first begin to grow 

 in the spring may be determined at the will of the cultivator. 



291. This is the key to some important practices in forcing. 



292. This should also cause attention to be paid to shading 

 buds from the direct rays of the sun in particular cases ; as in 

 that of cuttings, whose buds, if too rapidly excited, might 

 exhaust their only reservoir of sap, the stem, before new roots 

 were formed to repair such loss. 



293. As plants derive an essential part of their food from the 



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