530 SPECIAL DIFFERENCES AMONG SEEDS AND ROOTS. 



predominating ingredient, and it is connected with a large proportion of a 

 nitrogenous substance, resembling the curd of milk {casein), and with a 

 quantity of ash about equal to that in tlie pea, hut in which the phos- 

 phate of lime is said to be still more abundant. 



4°. In the potaioe — starch is the greatly predominating ingredient, but 

 it is united with albumen nearly in the same proportion as it is with 

 gluten in wheat. The inorganic matter is nearly in the same proportion 

 to the dry organic matter, as in the pea and the bean, but is much 

 more rich in potash and soda. Still it is more rich in the earthy phos- 

 phates than the ash left by wheat and oats, and is inferior in this respect 

 only to that of barley. 



5°. In the turnip — sugar and pectin take the place of the starch, and 

 these are associated with albumen, and with a proportion of inorganic 

 matter about equal to that of the potatoe, abounding like it in potash and 

 soda, but more rich in the phosphates of lime and of magnesia. 



6°. In the stems of the grasses and clovers — woody Jibre becomes the 

 predominating ingredient, associated apparently with albumen, and with 

 a larger proportion of inorganic matter than in any of the other crops. 

 In the straws and in some of the grasses which are cut for hay, silica 

 forms a large portion of this inorganic matter. In the clovers, lime and 

 magnesia take its place. 



The natural differences above described not only exercise an important 

 influence upon the mode of culture by which the different crops may be 

 most successfully and most abundantly raised, but also upon the way 

 in which they can be most skilfully and economically employed in the 

 feeding of stock. To tliis latter point we shall return hereafter. 



§ 27. Average composition and produce of nutritive matter per acre, by 

 each of the usually cultivated crops. 



1°. Average composition. — The relative proportions of the several most 

 important constituents contained in our cultivated crops vary, as we have 

 seen, with a great number of circumstances. The following table exhi- 

 bits the average composition of ] 00 parts of the more common grains, 

 roots, and grasses, as nearly as the present state of our knowledge upon 

 the subject enables us to represent it. (See table at top of next page.) 



In drawing up this table, I have adopted the proportions of gluten, for 

 the most part, from Boussingault. Some of them, however, appear to 

 be very doubtful. The proportions of fatty matter are also very uncer- 

 tain. With a few exceptions, those above given have been taken from 

 Sprengel, and they are, in general, stated considerably too low. 



It is an interesting fact, that the proportion of fatty matter in and im- 

 mediately under the husk of the grains of corn, is generally much greater 

 than in the substance of the corn itself. Thus I have found the pollard 

 of wheat to yield more than twice as much oil as the fine flour obtained 

 from the same sample of grain ;* and Dumas states that the husk of oats 

 sometimes yields as much as 5 or 6 per cent, of oil. We shall perceive 

 the practical value of this fact when we come to consider the uSe of bran 

 and pollard in the fattening of pigs and other kinds of stock. 



* Thus the four portions separated by the miller from a superior sample of wheat grown 

 in the neighbourhood of Durham, gave of oil respectively :-^fine flour, 1-5 per cent ; poUard, 

 2*4 ; boxings, 3-6; and bran, 3-3 per cent. 



