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 climaies 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 2 large scale. Root 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 
