CHAPTER XVI 

 LEAVES AND THEIR USES 



244. Growth of Leaves. — As a general rule, a leaf differs 

 from a branch in the fact that it can grow to about a certain 

 size and no larger. While a leaf is enclosed in the bud, the 

 cells divide but the leaf remains small, growing very slowly. 

 Long before the leaf unfolds, its cells have ceased to divide ; 

 the leaf has all the cells that it ever will have. Thus the 

 leaf remains with no further perceptible change until warm 

 weather comes in the spring, when its cells begin to grow 

 again, chiefly by the taking in of water ; little new living 

 matter is manufactured. The absorption of water can go 

 on rapidly, and this is why leaves unfold and grow so quickly 

 in the spring. 



Each leaf is capable of growing to about a certain size. 

 The exact size that a particular leaf will reach depends upon 

 a good many factors, among them the amount of food and 

 water that the plant can supply to it. So it happens that 

 the different leaves on a single plant may be very different 

 in size ; the leaves of a plant growing in dry soil may be 

 smaller than those of a plant of the same sort living in a 

 moist place ; and the leaves of a young tree are sometimes 

 much larger than those of an old tree of the same kind. 

 But in spite of all such differences, it is none the less true 

 that the size to which a leaf may grow is limited by the num- 

 ber of cells that it formed while it was shut up in the bud ; 

 although conditions may prevent it from reaching the full 

 size to which it might have grown, nothing can make it 

 grow beyond the limit set by the number of its cells. 



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