234 Studies in Forestry [CHAP. xi. 



decrease, five years later, was due to the fact that the richer 

 supplies of nutrient salts, rendered soluble and available as 

 food in the soil owing to the larger quantities of humus 

 formed after the fall of the coppice, began to get exhausted 

 after about four to five years' time. 



The argument is also, however, open to another grave 

 objection ; for the observations were confined to the lower 

 end of the stem, and were not continued all the way up the 

 bole. Now, Weise has shown that on Oak standards increment 

 becomes stimulated near the base of the stem, but that, when 

 undergrowth gets over twenty years in age, the basal incre- 

 ment decreases, whilst that near the top of the bole becomes 

 enhanced or, in other words, the top-girth becomes relatively 

 larger, so that the stem tapers less and has a higher technical 

 and financial value. 



The data with which the deductions under the second class 

 of experiments were supported, were found on examination 

 not to be reliable, as they were taken from mixed crops of 

 Pine and Spruce of equal age (probably formed by sowing), 

 in which the struggle between them had been so keen as to 

 prejudice the development of both species. Hence, in the 

 Scots Pine wood classed as without underwood^ the Spruce had 

 been removed in the thinnings ; whilst, in that shown as with 

 underwood, the Spruces were not truly underwood, but were 

 suppressed poles still struggling for life with the Pines, which 

 therefore showed less increment than they would have exhibited 

 under normal conditions. In other data, the areas reported 

 on were so small that general deductions were not justifiable ; 

 moreover, the average height of the stems (which in general 

 affords a very sound means of judging of the quality of the 

 soil ] ) showed that the areas not underplanted were somewhat 

 better than the others subjected to consideration. 



With regard to the third class of experiments, Michaelis 



1 Grebe, Ertrags- und Betriebsregehmg, 2nd edit. 1879, P- JI 4 



