KOOT-CROPS. 53 



amounts of produce, they must find within the soil a large 

 supply of available nitrogen. On the other hand, the large 

 amounts of produce obtained by the aid of nitrogenous 

 manures, on plots to which no carbonaceous manure has 

 been applied for about 50 years, is evidence that the atmos- 

 phere is at any rate the chief, if not the exclusive, source 

 of the carbon of the crops. 



The next Table (16) shows the proportion of leaf to root, Table 16 

 and the amount and distribution of certain constituents in ex P lained " 

 the root and in the leaf respectively. The results relate to 

 the mean produce of plots 6 and 4, with potash as well as 

 superphosphate as the mineral manure ; and they are given 

 for each of the five series — that is, with the mineral manure 

 alone, and with the various nitrogenous manures in addition. 

 Further, the results are the averages for six years, 1878-83. 



The first line of figures shows that the proportion of leaf Propor- 

 to 1000 root ranged from 152 to 216, and that it was the ^aL 

 highest with the highest manure, and the greatest luxuriance, leaf. 

 The proportion of leaf was considerably higher than in the 

 case of Swedish turnips, but very much lower than with 

 common turnips. With the same description of roots there 

 will, however, generally be the higher proportion of leaf the 

 heavier the soil, the wetter the season, the higher the nitro- 

 genous manuring, and the less ripe the crop. 



Eeferring to the percentage composition of the mangel Composi- 

 root and leaf, it is to be observed that whilst with turnips ^ °^Jf 0t 

 there was a much higher percentage of dry substance in the influenced 

 leaf than in the root, there is in the mangels, as there was ^ »«"»- 

 in the sugar-beet, a considerably higher percentage in the 

 root than in the leaf. The percentage of dry substance in 

 the mangel root is in fact considerably higher than in the 

 Swedish turnip root, whilst the percentage in the mangel leaf 

 is much lower than in the turnip leaf. The question sug- 

 gests itself, To what extent this may be due to more com- 

 plete exhaustion of the leaf in the accumulation of the larger 

 amount of reserve material, chiefly sugar, in the root ? 



The percentage of nitrogen in the dry substance of the 

 root is much the higher the higher the nitrogenous manur- 

 ing; indeed it is with the highest supply of nitrogen If 

 time as high as with the mineral manure alone. It will 

 be seen further on, however, that beyond comparatively 

 narrow limits a high percentage of nitrogen may even be a 

 disadvantage, so far as the feeding quality of the root is 

 concerned. As in the case of the turnips, the percentage 

 of nitrogen in the dry substance of the leaf is very much 

 higher than in that of the root, and it is the higher in the 

 leaf the less matured the root. 



