SPECIFIC GRAVITY OF BULBS. 329 



smallest proportion of water and the largest proportion of 

 nitrogen, and also other compounds, are those best suited 

 for our purpose. In the foregoing table it is seen that 

 the Swede turnip contained less water and more nutritive 

 matter than either of the others, and as Swedes are 

 always firmer and heavier than other turnips, it was 

 suggested that some good indications of these desirable 

 qualities might be deduced from the relative " specific 

 gravity" of the bulbs, and thus varieties of improved feed- 

 ing qualities be obtained. The* specific gravity of the 

 turnip has for some few years past, indeed, formed the sub- 

 ject of extensive practical experiments by the Marquis of 

 Tweeddale, and by Mr. Lawson, with the view of effecting 

 a permanent improvement in the quality of the crop. 

 They have for several seasons been in the habit of select- 

 ing turnips of the highest specific gravit}^, and planting 

 them for seed, from which again the heaviest bulbs were 

 selected and again planted, the produce thus increasing 

 materially in specific gravity in the course of a few years. 

 The question, then, as to the real nutritive value of the 

 roots was submitted to the chemist, as, practically, the 

 end sought for, the mere increase in specific gravity, might 

 be considered achieved. After a series of careful investi- 

 gations, it was found that in all cases the Swedish turnip 

 had a higher specific gravity than either the hybrids, 

 yellow or white varieties, but that no safe estimates 

 of nutritive value could be deduced from the mere specific 

 gravity of the root, which appeared to depend upon the 

 relative size of the cells in the mass of the root, and the 

 quantity of air contained in them. Therefore, supposing 

 it possible to displace the water, or a portion of it, and 

 replace it by air, the mass would immediately become 

 specifically lighter than it was, and yet have, for its weight, 

 a far higher nutritive value. In experimenting upon the 

 expressed juices of the bulbs, however, more satisfactory 



