CHEMISTRY OF THE CROP. 327 



in the tops or "shaws"from 79 to 90 per cent., or a mean 

 proportion of 85-5 per cent. This variation has a higher 

 importance than at first meets the eye ; it shows that the 

 largest crops are not necessarily the most valuable, as the 

 difference in weight per acre between two crops, may only 

 be due to the larger proportion of water in the one than 

 the other; and in this case the feeding value of the larger 

 crop would be absolutely less than that of the smaller, as 

 a proportion of its nutritive constituents would be con- 

 sumed in raising the temperature of the extra quantity 

 of water to the body heat of the animal, and thus contri- 

 bute nothing to its increase. Indeed, it is possible, taking 

 the two extremes, that a crop of 10 tons per acre may 

 contain absolutely a greater amount of keep than another 

 yielding double, or 20 tons per acre. 



In the ash, or inorganic constituents, even a greater 

 variation was met with; the proportions varying from *48 

 to 1-13 per cent, in the bulb, giving a mean of '73 per cent.; 

 and from 1*19 to 2'64< per cent, in the tops, or an average of 

 1'84 per cent. Thus the average percentage composition of 

 the turnip appears to be, in the bulb, 90 per cent, of water, 

 '73 per cent, of inorganic matter, and 9 a 27 per cent, of solid 

 organic matter consisting chiefly of sugar, gum, pectine, 

 nitrogen compounds (albumen), cellular tissue upon the 

 proportions of which the real feeding value mainly de- 

 pends. In the tops the average composition per cent, is 

 85'5 of water, 1-84 of inorganic matter, and 12*66 of solid 

 organic matter, consisting of the same substances, though 

 in different proportions, as is shown in the following 

 analyses. The composition of the inorganic portion (ash) 

 of the plant is given at top of p. 328. 



Basing our calculations on the foregoing mean propor- 

 tions of inorganic matter in the turnips, and taking the 

 average weight of the tops to be one-sixth that of the 

 bulbs, we should find that a crop of roots weighing 20 tons 



