The Growth of a Tree 



that gave up in their own good time the nuts which are the seeds 

 of the tree. 



The new shoots, having formed buds in the angles of their 

 leaves, rest from their labours. The tree had added to the height 

 and breadth of its crown the exact measure of its new shoots. 

 There has been no lengthening of limb or trunk But under- 

 ground the roots have made a season's growth by extending 

 their tips. These fresh rootlets clothed with the velvety root 

 hairs are new, just as the shoots are new that bear the leaves 

 on the ends of the branches. 



There is a general popular impression that trees grow in height 

 by the gradual lengthening of trunk and limbs. If this were 

 true, nails driven into the trunk in a vertical line would gradually 

 become farther apart. They do not, as observation proves. 

 Fence wires stapled to growing trees are not spread apart nor 

 carried upward, though the trees may serve as posts for years, 

 and the growth in diameter may swallow up staple and wire in 

 a short time. Normal wood fibres are inert and do not lengthen. 

 Only the season's rootlets and leafy shoots are soft and alive and 

 capable of lengthening by cell division. 



The work of the leaves has already been described. The 

 return current, bearing starch in soluble form, flows freely among 

 the cells of the cambium. Oxygen is there also. The cambium 

 cell in the growing season fulfils its life mission by absorbing food 

 and dividing. This is growth and the power to grow comes 

 only to the cell attacked by oxygen. The rebuilding of its tissues 

 multiplies the substance of the cambium at a rapid rate. A cell 

 divides, producing two "daughter cells." Each is soon as large 

 as its parent, and ready to divide in the same way. A cambium 

 cell is a microscopic object, but in a tree there are millions upon 

 millions of them. Consider how large an area of cambium a 

 large tree has. It is exactly equivalent to the total area of its 

 bark. Two cells by dividing make four. The next division 

 produces eight, then sixteen, thirty-two, sixty-four, in geometric 

 proportion. The cell's power and disposition to divide seems 

 limited only by the food and oxygen supply. The cambium 

 layer itself remains a very narrow zone of the newest, most active 

 cells. The margins of the cambium are crowded with cells whose 

 walls are thickened and whose protoplasm is no longer active. 

 The accumulation of these worn-out culls forms the total of tiic 



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