1 76 FORESTRY 



Stoppers for bottles and gaskets for or even of present-day matter-of-faet, 



engines. It is becanse it is so inipernie- a cell deep in the leg or arm of a man, 



able that it is ground up to make or hung high on the leaf of a tree, is in 



linoleum. A tree, from head to foot, essentially the same circumstance as a 



is armored against evaporation. Conse- primitive one-celled animal floating or 



quently its cells, though they hang in crawling about and absorbing its food 



the very eye of the sun, are in water, and air direct from the water. All cells, 



A tree manufactures its food direct animal or vegetable, are essentially 



from earth and air, a thing the animal alike in structure; they live on the same 



cannot do; and though it has no lungs, sort of food and take it in the same 



nor an\thing corresponding to such a way. It must be in liquid form; not in 



mechanical device, it feeds life's eon- mere suspension or emulsion, but in 



stant fires by taking in oxygen night true solution. As the cells in a man 



and dav. And how can a tree breathe are confined to one place, and cannot 



without lungs? float or wander in a stream or a pond. 



In a tree, the air enters through the nourishing stream is made to flow 

 openings called stomates on the bottom past them. It all amounts to the same 

 sides of leaves; but there are no air thing. Because our cells are so deep- 

 tubes continuing these openings for seated, so specialized, and so far from 

 the reason that the leaf is but a thin the free food and oxygen of nature, we 

 sheath of life, only a few cells thick have need of all this intricate machin- 

 and there are open spaces all through er)' and this digesting and food-prepar- 

 the inner structure in which air may ing laborator}'. But all the time it is 

 circulate freely. Along the sides of a the cells that are doing the living, and 

 tree, too, in the bark, are porous open- supporting and cooperating with one 

 ings, and these serve to let in air. The another in this strange stock company, 

 little short marks on the bark of birch, It is in this sense that Thomas Edison 

 and on the smooth exterior of plum is speaking when he says that "man is 

 and cherry, are such porous breathing a colony." Being, of all men, mechan- 

 placcs. While these lenticels are not so ical-minded, one might expect him to 

 e\ ident on the rougher trees, they are regard the human animal as a machine, 

 none the less there. But he is thinking of the builders and 



From the standpoint of evolution, operatives— the cells themselves. 



QUESTIONS 



1. What part of a tree is comparable in in raising water and minerals to the 

 function to the skeleton of an animal? tops of trees? 



2. Where are the living parts of a large . , i. ^ • i n j i i. 



. ^ ° '^ "4. In what ways are smgle-celled plants 



and animals like the living cells in a 



3. What are some of the factors at work tissue of a tree? 



