Agricultural Chemistry — Turnips, 559 



there exists a considerable amount of matter admitted by the 

 roots, with but little of special selective power, the proportions of 

 potass and soda may vary according to the variations in the soluble 

 contents of the soil, but the further we advance towards the ulti- 

 mate results of the organism, the larger is the proportion of potass 

 to soda ; there is in such a fact evidence against the supposition 

 that the vegetable organism can substitute the one alkali for the 

 other, for in the case assumed soda would seem to be present 

 only before the vital selective processes had been exercised upon 

 the matters brought within their sphere of influence. If, then, 

 the theory referred to suppose a replacement of potass by soda, 

 as an actual constituent of vegetable products, we think that facts 

 hitherto observed are such as should tend to disprove rather than 

 to prove its validity. On the other hand, we may well believe 

 that the large amount of mineral matters admitted into a plant, 

 beyond that which is likely to become fixed and combined with 

 its structures or deposits, has, nevertheless, some office to perform. 

 We know too little, however, of the means employed by the vital 

 processes to enable us to assign special agencies to special sub- 

 stances ; yet the presence of mineral matters not actually to take 

 part as constituents, is by no means improbably of essential im- 

 portance in determining the changes to which the circulating juices 

 of the plant are subject ; nor is it impossible that in such an office 

 as this soda may substitute potass, and one acid another, that is 

 to say, as agents, if not as constituents. It is, indeed, only by sup- 

 posing some other requirement in the plant than that of mere pro- 

 vision of actual constituents, that we can in any degree account either 

 for the extraordinary effects, which a large supply of mineral sub- 

 stances is in some cases found to produce, or for its possession of 

 the power by virtue of which so large an amount of such substances 

 is taken up by its roots and distributed throughout its living organs. 



It was our intention to bring forward many more results, both 

 of the field and laboratory, relating to the important subject of 

 root- culture, had our space permitted it. We have still eighty ash 

 analyses obtained from turnips, the history of the growth of which 

 is detailed in this paper. It would also have been advantageous 

 to give, in less technical language, a short summary of the results 

 arrived at in the course of these experiments, for the convenience 

 of those readers who are more conversant with practical than with 

 scientific agriculture. Having, however, through the kindness of 

 the Journal Committee, already extended our article to a length 

 beyond what is usually allotted to contributors, we must conclude 

 with a brief explanation of the means to be employed in the pro- 

 fitable cultivation of roots, and of the pecular properties which 

 they possess, and which constitute their value as fallow-crops. 



