the neighbourhood of pine plantations where self-sown pines have 
taken possession of much of the heath. Beneath the half shade of 
the growing saplings the heather is more robust in growth than in 
the open; doubtless as a result of the moderation of the harsh 
conditions of full exposure to the drying action of the wind and 
sun. 
The heath proper is characterised by the remarkable domin¬ 
ance of ling. It prevails over extensive areas to the almost total 
exclusion of any plant of a similar size and similar demands for 
light and soil. It characterises a plant grouping which is one of the 
most stable. The heath association occupies the lowest position 
among the vegetation of our country. It is the ultimate phase 
towards which all others move when in degeneration, owing to 
the deterioration of the soil either by the washing out of mineral 
food and the finest particles, or by the accumulation of sour humus 
at or near the surface of the soil. A lower stage than the Calluna 
heath to which this might pass has not yet been observed in this 
country. 
The conditions under which the heath exists are extreme. 
Though the rainfall of 30 inches in the year is adequate for 
ordinarily retentive soils, it is inadequate to supply a sufficiency 
of moisture to a soil that is coarse and open. During some 
period of the year, therefore, the soil of the heath is practically 
devoid of moisture, and the conditions are in effect those of the 
desert. The exposure to the heat of the sun and to the cooling 
and desiccating action of the winds, which pass unhindered and 
unchecked over the face of the heath, is extreme. The soil is 
dark, and has, therefore, a fair absorptivity for heat. It is also dry 
at times, and being largely composed of sand grains, then reaches 
■a considerable degree of warmth. The soil is covered by a thin 
compact layer of dry peat, generally only an inch or so in depth, 
though in constantly wet places this may attain sufficient thickness 
to be worth flaking off as “ turves ” for fuel. Below the layer 
of dry peat are a few inches of dark peaty soil, through which 
the roots of the heath plants ramify, in the main, horizontally. 
This dark root-searched layer is very often sharply marked 
off from the light coloured virgin subsoil by a “ pan,” or hard, 
ferruginous layer, which has been formed by the interaction of 
the peaty substances washed down by the rain from the surface 
with the iron salts common in the sand. The pan cuts off the 
vegetation from what store pf water and food there might be in 
the subsoil, and so contributes to the impoverishment of the soil. 
d he heath soil is typically poor in any kind of soluble mineral 
substance. 
1 he conditions determining the heath are thus the poverty 
m those mineral substances necessary to active plant assimilation, 
the lack and at times the almost total absence of moisture, and in 
a less degree the acidity of the soil, caused by the accumulated 
sour humus or peat. In a word or two, the master factors of the 
heath are drought, physical and physiological, and povertv. 
