CH. VII.] THE FRUIT AND SEED. 235 



sweeter and the higher is the fniit's flayoiir. Xo 

 fiiiits are so luscious as those grown witliin the 

 tropics, and the fruits of the temperate zone are excel- 

 lent in proportion to the brightness of its seasons. 



That light is essential in causing the colour of 

 the leaves and other parts of plants has been noticed 

 already ; and it aids the ripenmg process of fruit in 

 a similar manner, to convert their acid and mucila- 

 ginous constituents into sugar ; much carbon and 

 hydrogen have to be got rid of, and this is effected, if 

 light be admitted, by the evolution of cai'bonic acid 

 and watery vapour. How light operates in pro- 

 moting this and other decompositions which are 

 effected by the vegetable organs is at present a 

 mysteiT, but so it is ; and the gardener promotes its 

 access as much as lies within his power by removing 

 overshadowing leaves, by employing the best glass in 

 his hot-houses, and by havmg their interior whitened, 

 for white surfaces reflect all the rays of light back 

 upon the objects those smfaces enclose. 



The angle formed by the glass roof of the hot-house 

 is of veiy considerable importance, because rays of 

 light are reflected in proportion to the obliquity with 

 which they fall upon any given smface ; those which 

 fall upon it pei-pendicularly from the source of light 

 pass through \vith very slight diminution, but those 

 falling upon it in a slanting or oblique direction are 

 reduced in number in proportion to the obliquity of 



