70 BOTANY. [CHAP. ii. 



the welfare of its own members is very varied and 

 important from the point of view of animal life. The 

 exhalation of watery vapour into the air has already been 

 alluded to, and it has been proved that this function 

 influences to a very great extent the climate of a country. 

 Where forests have been cut down on a large scale, as 

 is frequently the case in newly occupied regions, the 

 springs have become less abundant or completely dried 

 up. On the other hand, where the rains are excessive 

 the climate has been rendered drier by the cutting down 

 of the forests. This was especially marked in the neigh- 

 bourhood of Rio Janeiro, where the climate was rendered 

 dry by the removal of the dense forest surrounding the 

 city, and eventually the rain had so much diminished 

 that the Brazilian Government were compelled to pass 

 a law prohibiting the further cutting down of trees. 

 Experiments have shown that a sunflower 3^ feet high, 

 weighing 3 Ibs., and with a leaf area of about 5,616 

 square inches, exhaled 20 ounces of liquid in the course 

 of a day ; a cabbage plant, with a leaf area of about 

 2,736 square inches, exhaled on an average about 

 19 ounces of water in a day. 



It is usually stated that green plants purify the atmo- 

 sphere from the point of view of animal life by removing 

 carbonic dioxide and restoring oxygen, and this is per- 

 fectly true ; but it is equally true that every plant also 

 gives off carbonic dioxide into the atmosphere and 

 removes oxygen, exactly as all animals do, and in con- 

 nection with the same function, that of respiration } or 

 breathing. A little attention to the fact that the 

 removal and restoration of carbonic dioxide to the 

 atmosphere is respectively the outcome of two distinct 



