200 AGRICULTURAL TEXT-BOOK. 



The nitrogen in the tops appears to average much higher than in the 

 bulb. 



442. A crop of 20 tons of bulbs or roots, and 4 tons of leave* 

 of turnips, mangel wurtzel, and carrots will respectively with 

 draw from the soil of an acre as follows : ( Way.) 



Turnips. M. Wurtzel. Carrot*. 



Phosphoric acid, - 45 Ibs. 21 Ibs. 39 Ibs. 



Sulphuric acid, 50 &quot; 22 &quot; 57 &quot; 



Lime, 90 &quot; 21 &quot; 197 &quot; 



Magnesia, 14 &quot; 22 &quot; 29 &quot; 



Potash, 140 &quot; 133 &quot; 134 &quot; 



Soda, 33 &quot; 70 &quot; 103 &quot; 



Chloride of sodium, 57&quot; 160&quot; 85 



429 &quot; 449 &quot; 664 &quot; 



443. Pectin, or Pectic acid (C II 0) (Solly} is a substance analo- 



1-2 8 10 



gous to gum, which exists in many plants, and especially in fruit. Itia 

 a tasteless solid, which swells up, and gelatinizes with water. It pos 

 sesses feeble acid powers, combining with bases to form pectatcs. Con 

 taining no nitrogen, it belongs to the heat or fat forming constituents cf 

 food and in this respect appears to act as an equivalent, in food, to 

 Starch. Pectic acid has been found in every plant for which it has been 

 sought for ; but in some it usurps the chief place, as in turnips, carrots, 

 beets, Jerusalem artichokes, onions, and in all kinds of fruits. It is 

 also found in the stalks and leaves of herbaceous plants, in the wood and 

 bark of all the trees examined, etc. Sec BouivingaultRuralEcon.p. 129. 

 fcreira on Food and Diet. Ch. ii. $ 6. 



444. The characteristics desirable in the turnip are hardiness 

 against insects and disease ; rapid growth 5 moderate size of 

 bulb ; and capability of keeping sound and fresh. Not only are 

 very large bulbs apt to be hollow, or cellular, but late examina 

 tions have shown that they contain, proportionally, less nutritive 

 matter than smaller ones : in some instances the difference was 

 as high as 50 per cent. In England some varieties are found 

 much more liable to disease than others ; and some retain their 

 flavor and solidity longer than others. In all these respects, the 

 Swedes appear to stand preeminent. 



