EMPIRICAL KNOWLEDGE 133 



as the cultivation of food-stuffs. The forester, 

 however, deals with a crop which takes the best 

 part of a century to mature, and in the nature of 

 things he cannot experience more than the fringes 

 of the matter. The mere empiricist must stop 

 much less than half way. The forester, in the 

 modern conditions, is in many ways taking liberties 

 with nature, and if he is not versed in the scientific 

 principles which underlie his work, he will surely 

 be defeated. The forester must apply the principles 

 of many sciences. He must have the aid of the 

 botanist. He must know the life-histories of the 

 trees, and he must know the principles on which 

 they grow. He must know the conditions needed 

 by the "light demanders," and he must know the 

 conditions under which the "shade-bearers" will 

 give their maximum yield, in the minimum time. 

 He must know which trees will associate with 

 others, and which trees are intolerant of any but 

 their own kind. Empirical knowledge of these 

 facts cannot be acquired in the time at the forester's 

 disposal. Then even in the natural conditions the 

 trees are subject to the attacks of parasitic fungi 

 which cause the destruction of the timber and 

 lead to the death of the trees. In the artificial 

 commercial forest the conditions favour the develop- 

 ment of those diseases, and if events are allowed 

 to take their course the forest may be destroyed. 

 Under present conditions in this country it is not 

 possible to estimate what the financial loss from 



