THE BOTANY OF THE APPLE TREE. 17 



It may serve to show the complexity of the apparently simple ap- 

 ple leaf to state that in a smallish leaf a little more than two and a 

 half inches long there are fully fifty millions of cells, of which no less 

 than eight millions constitute the skin of the two surfaces. In the skin 

 of the lower surface there are from 350,000 to 400,000 openings, the 

 breathing pores. 



The growth of trunk arid branches in thickness takes place in this 

 wise: During the latter part of spring and early summer there is a 

 great growth of soft cells between the wood and the bark, and imme- 

 diately the outermost cells begin changing to bark and the innermost 

 ones to wood. This continues until there is left but a thin layer of 

 the soft cells. The next year this thin layer grows rapidly and forms 

 a new mass of soft cells, which in turn develop into bark and wood, 

 and so on. Usually there is but one great growth of these cells in 

 each year, but in some seasons there are two growths, so that while 

 there is commonly but one ring of wood formed each year, now and 

 then there may be two. 



In this connection it may be well to state that after a stern is ripened 

 it does not elongate. All stories about the elongation of tree trunks 

 are founded upon erroneous observations, or are willful falsehoods. 



The growth of roots is, in nearly all respects, similar to that of the 

 twigs and branches. Here, however, there are no buds. The end 

 of the root is, however, much like the end of the stem inside of the bud. 

 If we should compare the tip of the stem in the bud with the tip of 

 the root, the difference would not be very great. Then, too, in the 

 root, as in the stem, the elongation ceases as soon as it has become hard 

 and firm. An old root never elongates its body. The growth in 

 thickness of roots is precisely like that of the trunk and branches, 

 and there are, consequently, similar annual rings of wood. 



With all this growth year by year there is a constant death of tis- 

 sues, which follows hard upon it. The layer of new wood is but 

 feebly alive by the end of the season of growth, and the new bark is 

 little, if any, better. The thin layer of soft cells between wood and 

 bark, that remnant of the previous year's active cells, the cambium of 

 the botanists, is all that retains much life. The pith and the medul- 

 lary rays are but passive storehouses at the end of the first year's 

 growth of a twig, and after that they are dead. In the buds the 

 outer leaves ("scales") soon die, leaving the tiny central stem, and the 



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