PRACTICAL INFERENCES. 115 



consequence is a yellow languid look about the leaves, 

 betokening starvation. On the other hand, excessive 

 size and succulence and too deep a green hue indicate an 

 excess of stimulant nitrogenous food and a deficiency 

 both of mineral food and carbon assimilation, in con- 

 sequence of which growth is arrested. In such cases the 

 amount of root-food taken up is out of proportion to the 

 .amount of leaf -food. If the season could be prolonged 

 so as to ensure a longer duration of leaf -action, the 

 balance might be adjusted, but this is rarely the case. 

 Appearances in such cases are apt to be misleading to 

 the inexperienced. There is an appearance of luxuriant 

 vegetation with which the intrinsic nutritive value of the 

 crop is not in accordance. 



Plants grown for Fibre, Apart from timber trees, 

 hemp and flax are the only two crops generally grown 

 on any large scale for their fibre, although the develop- 

 ment of the straw of cereals is dependent on the same 

 conditions. By hereditary transmission these plants 

 manifest a tendency to produce fibre in greater propor- 

 tionate amount than cellular tissue. Heat and light are 

 specially requisite to ensure the formation and proper 

 development of the fibre. Both are naturally plants of 

 hotter, drier, more luminous climates than ours ; never- 

 theless, if they can be grown rapidily they yield fibre, 

 although the secretions of oil, in the seed of the flax 

 (linseed), and of narcotic resin in the case of the hemp, 

 are not produced in a relatively sunless atmosphere. 



The formation of timber is, in general terms, the for- 

 mation of fibre on a large scale. Eoot development, 

 according to the special nature of the tree, of course 

 conduces to the formation and proper development of 

 leaves. Trees, from their root-range being wider than 

 that possessed by herbaceous plants, can collect food over 

 a larger area, and thus can extract nourishment from a 



