106 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
period during the months of September and October, as the 
young growths do not ripen properly, and are often destroyed 
by frost in the event of a hard winter succeeding such an autumn. 
Although rot in the wood of the larch is usually attributed to the 
condition of the soil, yet it is probable that improperly ripened 
wood may have equally as much to do with the disease ; while it 
appears to be almost a certainty that the blister so common in 
this tree is the effect of the same cause. 
The requirements of different species in respect to light should 
be well understood by the planter and thinner, as the mixing and 
mode of planting and thinning a plantation in a judicious manner 
depends a good deal on an accurate knowledge of this subject. 
Trees which require a considerable quantity of light for the 
development of their branches do best when planted by them- 
selves in masses, as if mixed with shade-bearing trees, the latter 
would be apt to crowd them out if both classes were of the same 
age. In growing oak on dry soils, however, its own shade is 
sometimes insufficient to keep down weeds and rubbish, which 
impoverish the soil by appropriating much of its plant food, and 
in order to prevent this, beech is sometimes recommended for 
planting under the oaks, when the latter have reached a height 
of 50 or 60 feet, and have received their final thinning, which has 
the effect of increasing the leaf canopy and enriching the soil. 
The same system might be adopted in regard to ash, as although 
the soil suitable for growing ash is of a damp nature, yet a 
greater crop of wood might be obtained from the ground than 
would be the case if the space beneath the trees remained 
unoccupied. Spruce or silver fir, however, should be substituted 
in place of beech, as the latter is of little value when small, and 
ash coming to maturity far quicker than oak, would not allow 
time for it to grow to any size. Oak, ash, larch, and Scots fir are 
the principal light-demanding trees; while beech, hornbeam, 
silver fir, and spruce grow well under shade. 
The annual rainfall of the district, considered in connection with 
the character of the soil, should influence our choice of plants to a 
certain extent. A porous, sandy soil is usually better suited for 
growing trees in a district with a heavy rainfall, than one of a 
cold retentive nature. In a moist atmosphere evaporation from 
the leaves is reduced to a minimum, and therefore the quantity of 
moisture required from the soil is comparatively small, while dry 
soils are more favourable to the development of fibrous roots 
