CONSIDERATIONS IN SILVICULTURAL RESEARCH 805 



I dare say it must be difticult for the non-scientific reader to picture 

 to himself an organ which functions both as the stomach and lungs at 

 the same time. However, I think I have already pointed out that this 

 is an ill-chosen simile. Likewise the author is not quite clear in his 

 mind concerning the two processes — photosynthesis and respiration. 

 As said above, oxygen enters into photosynthesis as a by-product, and 

 certainly is not combined with the water and soluble salts from the 

 roots and carbon dioxide to make starch and sugar. The presence of 

 oxygen in the leaves may also be due to respiration, but under those 

 conditions it has nothing to do with food elaboration. Speaking of 

 the raw sap coming up through the sapwood, the same author writes : 



"After being combined with water and oxygen in the leaves, the energy being 

 supplied by sunlight, the assimilated plant food passes down through the cam- 

 bium layer." 



Besides being a very incomplete statement of what happens in the 

 leaf, this passage contains substantially the same error as the foregoing 

 one. 



Still a fifth author writes: 



"Now all this time the leaves have been busy taking in carbonic acid gas from 

 the air. This they do by breathing. A tree breathes day and night through its 

 leaves and twigs and through small holes in the bark of the trunk; but most of 

 all through the leaves. The leaves combine the acid from the air with the water 

 and minerals from the soil. The raw food which the roots have sent up is 

 digested in the tree-top. 



"Without light and heat trees could not live, l^or the leaves serve as the 

 stomach of the tree, and they must have warmth and sunshine to help them 

 digest the tree's food. After the food is digested in the leaves it goes back to 

 the tree itself, ready to be used." 



This extract contains most of the errors already spoken of. Photo- 

 synthesis, respiration, and digestion are hopelessly confused. 



The last example I wish to cite is the case of a forester who wrote 

 a paper dealing with the importance of street trees and the many im- 

 portant reasons why they should be planted in the streets. One of 

 the benefits which he mentioned was the fact that the leaves of the 

 trees absorb great quantities of atmospheric moisture from the air and 

 in this way drain the air of humidity, thus making a hot, sultry, humid 

 day drier and more bearable to city inhabitants. 



Were I to take such a collection of passages from a lunnber of pop- 

 ular nature-study books written for children by unscientific authors, I 

 would not be surprised. I'.ut 1 am positively astonished to find such 

 statements as these made l)y competent foresters, all of whom are 



