32 LEAVES. 



of being converted into the different substances 

 required for the growth of the plant and the 

 production of its fruit and seed. 



The Hght of the sun striking on a leaf causes 



1. Decomposition of carbonic acid, by which 

 carbon in different vegetable forms enters into 

 the composition chiefly of the solid parts of the 

 plant — this is in proportion to the intensity of 

 the light to which it is exposed ; hence, plants 

 grown in the shade are weak, and vice versa. 



2. Extrication of nitrogen. 



3. Insensible perspiration or evaporation; 

 hence this does not take place during the 

 night. 



The health of plants depends much on the 

 proper adjustment between the quantity of 

 juices taken up by the roots, and the perspira- 

 tion of the leaves. If they are exposed to too 

 much solar light, the perspiration is greater 

 than the roots can supply, and the leaves flag : 

 when transplanted, if watered in the evening, 

 the roots become supplied with moisture and 

 juices, the perspiration ceasing during the night, 

 this action recovers its equiUbrium, and the 

 leaves are seen erect in the morning. 



The quantity of light or shade which can be 

 borne by a plant, depends on the number, form 



