Agricultural Chemistry — Tarnips. 



553 



Such substances, indeed, may perhaps be considered as still be- 

 longing to the mineral kingdom, upon which animal life cannot be 

 sustained. 



Referring to the more special lesson of the experimental results 

 last given, we notice, that whilst the leaf grown by farm-yard 

 dung contains 3 -60 per cent, of nitrogen in its dry matter, that 

 grown without manure of any kind in a turnip-bulb exhausted 

 soil has 4-35 per cent ; and it will be remembered, the bulbs cor- 

 responding to these specimens of leaf give respectively 1 '56 and 

 3-31 per cent. We have, then, in the leaf as well as in the bulb, 

 a larger proportion of nitrogen in the more natural but agricul- 

 turally useless turnip than in the cultivated one ; and if we are 

 right in considering that, within certain limits, the composition of 

 a succulent imperfectly elaborated vegetable will bear some direct 

 relation to the supplies of food within its reach, we must conceive 

 that there was, independently of art, a resource of nitrogen avail- 

 able to the uncultivated plants far beyond that of other necessary 

 constituents. If, then, the powers of reliance upon normal sup- 

 plies of nitrogen here observed are to be fully developed and 

 turned to economical account, it is more especially by means of 

 an artificial provision of the other constituents that this object will 

 be attained. 



We think that in these facts we have a beautiful illustration of 

 some of the physical and physiological characters upon which 

 depend, materially at least, the economic value of the turnip in 

 rotation with corn. The true economy of alternate cropping, 

 whilst, however, it is intimately associated with functional differ- 

 ences, such as we have shown to exist in the selected plants, yet 

 depends much also upon the destination and uses of the produce, 

 independently of which, the peculiar accumulative tendencies of 

 the different crops could not be rendered profitably subservient. 

 We shall not, however, consider the connexion between the various 

 sources of the economy of a rotation of crops, until, having detailed 

 all the evidence which it is our intention to bring forward, we 

 come to sum up and apply our departmental results to the prac- 

 tice of agriculture. 



We shall now g-ive some account of the mineral substances 

 found in the turnip. Our experimental results referring to this 

 branch of the question are very numerous, and it was our wish to 

 have considered them somewhat fully ; but as our permitted space 

 is already nearly exhausted, we must defer doing so until a 

 future opportunity, and confine our remarks on this occasion to 

 some explanation of the nature of the subject, and to indicating 

 the general bearing of our evidence upon the conclusions which 

 have been arrived at in the foregoing pages. 



