40 TRAXSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



profit every year or at most every few years, but the forester 

 receives no money return on an individual crop until a period 

 of some sixty or more years, after which time the money invested 

 in initial and recurrent expenses must be retrieved at compound 

 interest before any profit can be realised. Hence all operations, 

 especially those undertaken at the commencement of the 

 rotation, must be confined to a minimum financial outlay not 

 more than may be reasonably expected to be repaid for by 

 increased tree-growth ; that is to say, manuring, ploughing, or 

 any except the simplest ameliorative operations are prohibited. 

 In other words, direct control of the soil conditions is almost 

 entirely impossible; we must take the soil as it lies; but if 

 we cannot modify the soil we must modify the crop. Although, 

 owing to the greater value of his produce, the farmer can 

 modify the soil to a great extent, he bows before the same 

 necessity as regards climatic conditions always, but as regards 

 soil only to a small degree ; while in the still more intensive 

 cognate operation of culture under glass, both soil and climate 

 are so completely under control that practically any crop may 

 be grown. 



This point indicates the essential difference between agri- 

 cultural soil science and forest soil science, and at the same 

 time puts us in the proper position from which silvicultural 

 practice may be reviewed in relation to soil conditions. Agri- 

 cultural soils are suited to the growth of agricultural crops, 

 forest crops must be planted on the soil for which they are 

 fairly exactly suited ; the farmer has chosen his soil, we must 

 choose our crops ; the forest soil has no status as such apart 

 from the species which will thrive on it, it is a medium of 

 growth for one or more definite species ; the physiological 

 idiosyncrasies of individual species are of as much importance 

 to the forest botanist as are general principles of plant nutrition, 

 hence forest soil investigation must always be correlated with 

 the growth of individual species of trees as well as of trees 

 as a whole. The crops of the farmer have all an ecological 

 family resemblance ; those of the forester are exceedingly variable 

 in their demands and effects upon the soil. Agricultural soil 

 science is almost wholly limited to the study of soil conditions 

 and mesophytic plant growth. Forest soil science is more 

 properly the study of "soil conditions and plant growth" in 

 general. 



