AIR AND LIGHT. 63 



And if buds that are very torpid are exposed 

 to direct light, they will be stimidated into 

 action. 



So that what parts of a tree shall first begin 

 to grow in the spring may be determined at the 

 will of the cultivator. 



This is the key to some important practices 

 in forcing. 



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 ex- 

 haust their only reservoir of sap, the stem, 

 before new roots were formed to repair such 

 loss. 



As plants derive an essential part of their 

 food from the air by the action of light, it fol- 

 lows that in glass-houses those which admit the 

 greatest portion of light are the best adapted for 

 purposes of cultivation. 



And as it has been found by experiment, 

 that light passes more freely through a cur- 

 vilinear than through a plane roof, and through 

 glass forming an acute angle with the horizon 

 than through perpendicular glass, it follows that 

 a curvilinear roof is best, and a plane roof with 

 glass perpendicular sides the worst adapted to 

 the purposes of the cultivator. 



