CONSIDERATIONS IN SILVICULTURAL RESEARCH 803 



ments. We find in them not only crude similes and misleading state- 

 ments concerning the fundamental life processes of the tree, but we 

 find actual misstatements of fact. To illustrate my point I have selected 

 at random a few passages from about a half dozen recent forestry 

 books, both elementary and advanced in character, all of them written 

 by either practicing foresters or professors of forestry. Since here 

 also I am dealing with a system or policy and not with individuals, it 

 is neither necessary nor desirable to mention the authors' names nor 

 the titles of the books. 



The first passage I happened to come to was this one : 



"The leaves are the stomach and lungs of the tree. Their broad blades are 

 a device to catch the sunlight which is needed in the process of digesting the 

 food of the tree. . . . The green pigment, chlorophyll, in the leaf is the 

 medium by which, with the aid of sunlight, the sugars are manufactured." 



To speak of the leaves as the stomach and lungs of the tree is to 

 employ two very unfortunate and farfetched similes, the accuracy of 

 hoth of which must be doubted. The stomach in the animal body is 

 the organ of digestion. The plant has no organ in which the digestive 

 process is centralized ; digestion is closely associated with the food 

 storage centers and these may be in widely separated parts of the tree. 

 Likewise the breathing process in the plant is not localized in the leaf ; 

 certainly there is no diaphragmatic movement during the breathing pro- 

 cess as in the animal body. Therefore it is misleading to refer to 

 respiration in plants as "breathing." Furthermore, sunlight has nothing 

 to do with the process of digestion, which is carried on, as in the animal 

 body, by means of ferments or enzymes. So far as is known, sugars 

 are not manufactured in this way; a very simple carbohydrate — for- 

 maldehyde — is the first product. This is elaborated into starch and 

 the starch is changed to sugar for the purpose of translocation. The 

 same author, speaking of stomata and lenticels, writes : 



"These pores are necessary for the breathing of the tree (respiration), whereby 

 carbonic acid gas is taken in from the air and o.xygen given out. The process 

 of assimilation depends upon this breathing process, and it is therefore evident 

 that when the stomata are clogged, as may occur where a tree is subjected to 

 smoke or dust, the life processes of the tree will be interfered with. The same 

 injurious effect results when the stomata of the roots are interfered with." 



Here the same author sadly confuses two separate and distinct physi- 

 ological processes of the tree — respiration and photosynthesis. Respira- 

 tion, of course, does not consist of taking carbonic acid gas from the 

 air and giving off oxygen. This is a popular misconception. The 



