122 PLANT LIFE ON THE FARM. 



sunlight are lacking, the chlorophyl is not formed in suffi- 

 cient amount, or is imperfectly developed, and the consequence 

 is a yellow languid look about the leaves, betokening starva- 

 tion. 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 consequence 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 grown in this country 

 on any large scale for their fibre, although the development 

 of the straw of cereals is dependent on the same conditions. 

 By hereditary transmission these plants manifest a ten- 

 dency to produce fibre in greater proportionate 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 ; nevertheless, if they can be 

 grown rapidly 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 our relatively 

 sunless atmosphere. 



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

 tion of fibre on a large scale. Root development, according 



