The Ecology o/Calluna vulgaris. 235 
thickest towards the middle of the heather and thins out towards 
Y x , being practically absent at Y 2 , where solid chalk occurs 1 foot 
4 inches below the surface. The distribution of the heather on this 
side appears to be determined by the depth of clay-with-flints 
present, but at Y 7 , where Ccilluna is very thick and quite 2 feet high, 
the plants were rooting down into the chalk rubble 16 inches below 
the surface, and penetrating lumps of chalk. These roots appear 
to be functional and healthy and contain mycorhiza. 
Section X shewed a similar distribution of the clay-with-flints, 
thickest in the heather area and thinning out on the slope of the 
down towards the N.W. 
Table 1 shows the nature of the soil and the percentage of 
calcium carbonate present in the soils from some of the holes at 
depths of 6 inches and 12 inches respectively. 
The percentage of calcium carbonate present is very low all 
over the heather area. Although this is the case and the spread of 
Calluna appears to be definitely related to the distribution of the 
clay-with-flints over the chalk, small lumps of the latter occur 
within the rooting area. 
The root system of the heather is contained chiefly within the 
first 12 inches of soil, but as noted above, in some of the holes, 
roots were growing into the chalk rubble and were apparently 
functional. 
Calluna is recorded from limestone soils in various part of Great 
Britain and Ireland, although it is well to remember that a soil on 
limestone is not necessarily rich in calcium carbonate unless the 
rock is near the surface. 
Taking into account the somewhat conflicting horticultural 
evidence, which records species of Erica usually regarded as 
calcifuge, and also Diantlius alpinus, as growing well on certain 
limestones, although refusing to do so on chalk, and also Graebner’s 
explanation of the behaviour of calcifuge plants towards lime, the 
present work seems to favour the view that factors other than the 
percentage of CaC0 3 present are involved in the soil preferences 
shown by so-called “ lime-shy ” plants like Calluna, although it does 
not support the conclusion that Calluna cannot compete success¬ 
fully on soils containing a high proportion of soluble mineral 
matter. 
II. A preliminary analysis indicated a relatively high proportion 
of magnesia in the soil in which the heather was growing. As it 
was thought this might possibly have some significance in regard 
