ROOT-CROPS. 19 



SECTION L— EXPERIMENTS WITH ROOT - CROPS 

 GROWN CONTINUOUSLY ; BARN FIELD, ROTH- 

 AMSTED. 



Introduction. 



The Boot-crops, the conditions of growth and the composi- Conditions 

 tion of which we have first to consider, include members of °f growth 

 more than one natural Order of plants ; and they are grown crops. 

 for, so to speak, certain intermediate parts and products, 

 which are, by cultivation, very abnormally developed ; whilst 

 the crops are not allowed to ripen, but are taken when in a 

 succulent and immature condition. We shall thus have in- 

 teresting points of comparison, or contrast, brought out, as to 

 the conditions of growth of these crops, and of those to 

 which we owe ripened products, such as the cereal grains. 



The crops to which we shall specially direct attention are — 

 some varieties of turnips belonging to the Order Cruciferse, 

 and two varieties of beet, namely, the sugar-beet, and the 

 feeding mangel, of the Order Chenopodiaceae. 



The introduction of turnips into our rotations may be importance 

 said to have been one of the most important improvements °f turni P 

 of modern times. The growth of the crop constitutes in- 

 deed an essential element, not only in the ordinary four- 

 course rotation, but in all our varied rotations. 



From certain characters of the turnip plant, and of other Root-crops 

 root-crops, especially their abundant leaf -surface, and from andni ^'°- 

 certain conditions of their growth, it has frequently been 

 assumed that they are largely dependent on the atmosphere 

 for their nitrogen ; and that they are in fact thus collectors 

 of nitrogen for the crops grown in alternation with them. 

 But we shall see that experimental evidence does not support 

 this conclusion ; and that we must look in other directions 

 for an explanation of the undoubted benefits of the growth 

 of root-crops in rotation. 



The object to be attained in the cultivation of root-crops is Abnormal 

 to encourage, by artificial means, a quite abnormal develop- l 00 ^™ 1 ' 

 ment of a particular part of the plant. If, for example, the 

 turnip-plant were grown for its natural seed-product— oil — a 

 heavier soil would be more suitable than when the object is 

 to develop the swollen root. In our climate a biennial habit 

 would be induced, and it would be so grown as to be exposed 

 to the summer temperature at a later stage of the life-history 

 of the plant — that is, at the seed-forming and ripening period. 

 Under these circumstances there would be much less of 

 fibrous root distributed through the surface-soil, the main 

 root would be much more fusiform, tapping rather than 



