AGRICULTURAL TEXT-BOOK. 211 



things being equal, varies in the weight per acre, according to 

 variety, more than perhaps any other cultivated plant. The 

 quantity of starch is at its maximum in the winter. In the 

 spring, vegetation becomes active, and the buds begin to grow at 

 the expense of the starch contained in the tuber. Hence, at this 

 season, potatoes are less mealy, and, in consequence, less es 

 teemed for eating. The tissue of the potato consists of a mass 

 of cells, and in these the starch is stored up in the form of grains, 

 of the ordinary shape, and these congregate principally in a zone 

 near the skin, and are less abundant toward the center; the re 

 maining space, in and between the cells, is occupied by a thin 

 albuminous liquor, constituting three-fourths of the total weight 

 of the tubers. All the nitrogenous matter is dissolved in the 

 juice, and consists almost entirely of albumen, with a very small 

 quantity of aspcuragin and free acids. The substance of which 

 the cells consist is essentially different from that found in other 

 plants. It possesses the property of swelling in water into a 

 translucent jelly, and of being transformed into sugar and gurn 

 by the action of acids, and consequently occupies a position in 

 termediate between starch and woody fibre. Potatoes are rea 

 dily frozen at a few degrees below freezing point, and when 

 again thawed are soft and sodden, and allow the greater part of 

 the juice to flow out in fact, the cells are burst by the ice formed 

 within them, the organic structure is destroyed and vitality lost ; 

 while decay speedily succeeds. A chemical change, when the 

 freezing has been gradual, is often perceptible ; the tubers ]&amp;gt;?- 

 coiae remarkably sweet, and contain an appreciable quantity of 

 uncrystallizable sugar. 



4fr&. Ultimate ANALYSIS of the Potato: ( Bowsing ault.) 

 Cnrboa, - - 440 \\ W ate r, - - 759 



Hydrogen, - - 5.8 jj S &amp;lt;lid irnttei dried at 230 



Oxygen, - - 44.7 jj Aar. in tacno, - 24.1 



Nitrogen, - 1.5 jj . 



Ashes, - 4.0 (I 100.0 



From ihU we RP that the proportion of Nitrogen is very small ; but 

 it is still smaller in potatoes that have been kept for aotno time. 



