I'OREIST GROWTH 81 



avoided, and the roots grown near together. The 

 apphcation of sulphate of potassium and superphos- 

 phate is generally necessary if roots containing a large 

 percentage of sugar are desired. 



Potatoes are surface feeders, and require a liberal 

 general manuring to ensure an abundant crop ; farm- 

 yard manure is thus generally employed. Very good 

 results are given by a mixture of sulphate of ammonium, 

 superphosphate and sulphate of potassium ploughed in 



before sowing. 



i 



Forest Growth. — The figures given in the table 

 represent the composition of the produce of beech, 

 spruce fir, and Scotch pine forests felled for timber, 

 and are the results of extensive investigations made in 

 Bavaria. 



The amount of dry matter in the annual forest 

 growth is in excess of that yielded by any of the 

 cultivated crops given in the table, excepting mangels. 

 This large produce is obtained by a very small con- 

 sumption of soil food; the amounts of potash and 

 phosphoric acid required are especially far less than in 

 the case of any farm crop. The greater part both of 

 the ash constituents and nitrogen annually assimilated 

 is returned to the soil in the fallen leaves ; if these are 

 left undisturbed, and allowed to manure the ground, 

 the requirements of the forest become extremely small, 

 far smaller than in ordinary farm culture. It appears 

 that about 3,000 lbs. of perfectly dry pine timber are 

 produced with a consumption of only 2 J lbs. of potash, 

 and 1 lb. of phosphoric acid per acre per annum : with 

 beech timber the quantities required are rather larger. 

 The amount of nitrogen in timber is vcrj small ; the 

 6 



