PRACTICAL INFERENCES. 113 



sible, short of frost, and what is of even more impor- 

 tance, kept as uniform as possible. By such means the 

 roots may be kept dormant, and the waste to the farmer, 

 which would occur from the unseasonable growth of the 

 plant using up the food intended for his cattle or sheep, 

 obviated. 



Plants Cultivated for their Foliage, Among these 

 are the various green crops and forage plants, cabbages, 

 mustard, clovers, sainfoin, lucerne, vetches and pasture 

 grasses. Apart from the special requirements of each 

 particular 'plant, such as the special influence of nitro- 

 genous manures in promoting leaf -growth among grasses, 

 and of mineral manures in fostering the leafy develop- 

 ment of leguminous plants, and the special demands 

 made by particular circumstances, the object, in all cases, 

 is to ensure a rapid, abundant and nutritious leaf -growth. 

 In some cases where otherwise too great acridity might 

 be produced, it is desirable to secure shade to the leaves, 

 and thus prevent the formation of the objectionable 

 matters. Thus, in the case of cabbages the grower pre- 

 fers those which "heart" well, i. e., those in which the 

 leaves are tightly packed one over the other, and do not 

 readily separate ; and this tendency is increased by con- 

 stantly selecting for seed those varieties in which this 

 peculiarity is seen to be most marked. At other times 

 the production of objectionable secretions is obviated by 

 the process of " earthing up," as in* the case of celery, or 

 by tying up the leaves as in lettuces. 



The development of leaves is of course largely depen- 

 dent on the well-being of the roots, so that, in a general 

 way, all those conditions of soil which are propitious 

 to the development of roots are so also to that of leaves. 



The requirements of particular plants are so varied, 

 according to their affinity and the very diverse modifica- 

 tions of form and structure presented by their roots., that 



