168 USES OF LEAVES. 



EDWARD. 



But if the leaves are so useful, why do not the 

 trees die when they fall off? 



MOTHER. 



When vegetation ceases, that is, when the 

 plants do not continue to grow, as is the case with 

 many of them during the winter in this country, 

 the leaves become unnecessary, and then fall off or 

 decay ; but when warm weather approaches new 

 ones appear, and the plant begins to grow again. 

 The under side of leaves is furnished with a great 

 number of little vessels, or tubes, which seem to be 

 intended to imbibe the moisture of the air. M. 

 Bonnet, indeed, proved this by a very simple ex- 

 periment : he placed a leaf of the white mulberry, 

 Mo'rus al'ba, with its upper surface upon water, 

 and found that it did not continue fresh and green 

 for more than six days ; but another leaf of the 

 same tree, placed with its under surface upon 

 water, continued fresh for six months. The upper 

 surface of the leaf serves as a defence to the under 

 side ; and this position of the two surfaces appears 

 to be essential to the health of the plant ; for if a 

 branch be turned upside down, in such a manner 

 as to reverse the natural situation of the leaves, 

 they will turn back again of themselves. 



But we must not forget the fourteenth class, 

 where we left off. You can now, probably, under- 



