CHAPTER IV 



THE NUTRITION AND FOOD-SUPPLIES OF 

 WOODLAND CROPS 



'Concerning the growth of plants a large amount of informa- 

 tion lias been amassed, but we are far from possessing even an 

 approach to a knowledge of the laws which regulate this 

 important subject.' ROSCOE'S Elementary Chemistry^ 1888, 

 page 413. 



ALL plant life is governed by what is known in agricultural 

 chemistry as the Law of the Minimum. According to this 

 law the essential factor occurring in minima regulates the total 

 extent of production ; whilst any given species of plant attains 

 its finest growth and development in localities where all the 

 essential factors are most favourably combined. These essential 

 factors are partly of a physical, and partly of a chemical 

 nature. To the former belong the action of warmth and 

 of light, and to the latter carbonic acid, oxygen, and the 

 water requisite for dissolving and holding in solution the 

 mineral nutrients that can only be absorbed by the plant in 

 the shape of soluble salts. 



Temperature makes itself felt, throughout both the soil and 

 the atmosphere, in calling into activity the process of vegetation 

 in spring, and in continuing it during the summer and the 

 autumn. Most of the trees indigenous throughout central and 

 northern Europe begin their period of active vegetation in 

 spring when the temperature rises to 6 or 8 C, although with 

 exotics from the warmer south a higher temperature is requisite 

 in order to stimulate them to activity. 



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