78 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
are of especial interest, as showing what is evidently the influence 
of the humus layer in counteracting or modifying the effect of 
variations of season. While no particular year, for instance, is 
especially marked as promoting or retarding the growth of those 
where this layer exists (Lot I), the years 93 and 96 are par- 
ticularly conspicuous by the maximum growth of the majority 
taking place in the former, and the minimum in the latter year in 
Lot IL, where the surface is grassy and exposed to sun and wind. 
In the larch (Lot III.) the year ’96 also exercised considerable 
influence, with a similar result to that noticed in Lot II., but the 
maximum chiefly occurs in the damp season of ’94. In the 
unthinned larca (Lot IVa.) the minimum is found in four trees 
out of fivein 96, The remaining lots call for no special comment. 
The most striking fact in connection with these trees, however, 
is the almost invariable decrease in the production of summer 
wood in ’96, while the dry summer of 793 rather favoured the 
formation of this zone than otherwise. In eighteen trees out of 
twenty larch and Scots pine of twenty years of age, the minimum 
breadth of this zone occurred in ’96; while in fourteen out of the 
same number the year ’93 produced the greatest bulk of summer 
wood. As with the total breadth of the ring, so with the summer 
wood zone, season had no predominant influence in the case of the 
ten Scots pine, the roots of which were protected by a humus 
layer; while with those not so protected the majority attained 
the maximum breadth in ’93 and the minimum in’96, In the 
larch (Lot ILI.) the maximum and minimum ring breadihs and 
summer zones coincide. 
Coming to the hardwoods—beech and oak—it is apparent that 
the same climatic influences produce different results in these trees 
to those noticed in the conifers. In the trees examined of both 
these species, the (popularly termed) growing season of 1894 is 
conspicuous by reason of the small amount of wood produced in 
that year in eight out of the ten oaks in Lot VI. growing on stiff 
soil, and in three out of the five growing among beech on light 
soil. The maximum breadth occurred in seven trees in the former 
lot in 1895, and in that year in the whole of Lot VIJa., while in 
those standing among beech 793 shows the best result. It must 
be noted, however, that the oaks in ’93 were visited in spring by 
a strong attack of the oak-leaf roller moth, and it is very likely 
that those in question suffered from this attack, and the natural 
course of growth would be disturbed. ‘This is the more probable 
