118 THE COMPOSITIOX OF CROPS IN 



somewhat wider reference to others. In the case of potatoes 

 the discrepancies between the older and later analysts are con- 

 siderable, arising probably from want of sufficient precaution in 

 the process of ignition by which the ash is obtained for analy- 

 sis. In so far as sulphur or sulphuric acid is concerned, it is 

 doubtful whether the average results yet arrived at are quite 

 satisfactory. In the cases of beans and pease the averages 

 given rest on narrower bases than those stated in the other 

 cases. Moreover, the crops per acre of these leguminous plants 

 vary so widely according to the character of the season and 

 other circumstances that it is almost impossible to say what are 

 average crops even on soils suitable for their cultivation. The 

 weights of produce per acre in all cases are meant to represent 

 good average crops ; but not necessarily the average of the 

 actual produce of the country generally. For several reasons, 

 which need not be stated, it has been deemed advisable to take 

 such crops as would be produced on fairly good soil in a good 

 state of cultivation. From the weight of crops here given, the 

 composition of crops of somewhat greater or somewhat less 

 weight per acre, can easily be calculated by "simple propor- 

 tion " ; but it must not be assumed that the composition of a 

 good crop will, relatively to gross weight, represent quite accu- 

 rately the composition of an inferior crop of the same plant. 

 The average produce of straw in the cereal crops can be esti- 

 mated with some approximation to accuracy ; but it is obviously 

 more difficult (even with some amount of data at command) to 

 fix on the average relative weight of tops and bulbs in the case 

 of turnips, while in the potato crop the weight of haulms 

 depends on the stage of maturity (not to speak of disease) at 

 which the crop may have arrived when dug up. In this crop, 

 however, the weight and composition of the tops are only of 

 subordinate importance. The relative proportions that we have 

 taken for grain and straw bulbs and tops, &c., are as follows : — 

 Wheat, grain to straw as 1:1-6; barley, do. as 1 : 1*4; oats, do. 

 as 1 : 1'3 ; turnip bulbs to tops as 1 : 0'27 — that is, the tops are 

 taken at between one-third and one-fourth of the bulbs. That 

 may be deemed a moderate average for tops, and implies that 

 the crop has arrived at a fair condition as to maturity. Potato- 

 tops uncertain, but taken at one-sixth of the weight of the 

 tubers. Beans and pease ; — very little satisfactory evidence to be 

 had ; but, following the estimates of Stephens {Book of the Farm) 

 and others, one ton of straw per acre is assumed in both cases. 

 We give, however, the constituents of grain, roots, &c., separately 

 from those of straw and tops : for many purposes the amount of 

 nitrogen and mineral matter drawn from the land by the former 

 only may be deemed of importance, inasmuch as the greater 

 part of the materials which go to the formation of the latter 



