552 



Agricultural Chemistry — Turnips. 



matter of the leaf has a percentage of nitros^en twice as high as 

 that of the bulb. A given weight of the fresh leaf would there- 

 fore contain more than three times as much nitrogen as an equal 

 amount of bulb. Since, however, the bulk of the leaves at the 

 time the turnip crop is gathered or consumed are past the condi- 

 tion in which our picked specimens were taken for analysis, it 

 would be unsafe to employ these results for purposes of acreage 

 calculation ; yet they are in other respects to be relied upon. 



Comparing the characters of the cultivated with those of the 

 uncultivated plants, as shown by the analyses which have been 

 given, we observe the decrease by cultivation in the percentage of 

 nitrogen in the dry matter is in the leaf only '7b, but in the bulb 

 1*75 ; from which, again, we may perhaps gather that the cul- 

 tivated bulb is the result of a continued accumulation of secreted 

 matters, formed in quantity beyond the essential requirements of 

 the plant as such : the leaf, on the other hand^ containing, besides 

 its own special structures and products, little more than those sub- 

 stances derived from immediate supply, — has, therefore, a com- 

 position in a less degree varying according to the constant 

 circumstances of growth, but comprising a larger proportion of 

 unsecreted matter. 



The fact that, notwithstanding the large nitrogenous contents of 

 turnip-leaves, they should only be to a small extent valued as food, 

 doubtless arises from the large amount of matters which they con- 

 tain only brought within the range of the organism, themselves as 

 yet unorganised, and existing as saline and other changeable 

 fluids, to w^hich we may readily attribute a medicinal and purga- 

 tive, rather than a direct nutritive effect ; elaboration to some 

 extent being, as we are aware, an important element in the con- 

 dition of food for animals. The low degree of stability in some 

 of the nitrogenous contents of succulent substances, as indicated in 

 the drying process, as well as our conceptions of the offices and 

 physiological position of the different parts of a plant, bespeak, 

 indeed, that where an active circulation is still proceeding, there 

 will be found not only the actual and fixed, but also the prospec- 

 tively possible constituents, the latter as yet only in a vehicular 

 condition, and little influenced by the selective and appropriative 

 powers of the organism. It is true that the varying character of 

 the vital apparatus of different animals adapts them to the use of 

 vegetable food in varying degrees and states of elaboration ; but 

 there seems to be a point in this degree of elaboration below 

 which constituents lose their food-qualities ; or even, it may be 

 doubted whether, in such cases, the matters are not really as little 

 truly vegetable as would be the watery extract of the soil as it is 

 taken up by the rootlets, and from the condition of which little 

 deviation has hitherto resulted from the vital actions of the plant. 



