118 HEART-ROT 
from other woods. A rootstock sent me from Tintern 
showed the same phenomenon, and a wind-blown larch on 
the Endsleigh estate had been rotted solely through its 
tap-root. 
We are thus confronted with the fact that the disease 
enters the trees through roots—either the tap-root or 
‘anchor ’ roots—which grow more or less vertically down- 
wards and penetrate the subsoil. With this in view I had 
a trench cut 3 ft. deep in order to ascertain the state of 
the roots in the subsoil. The superficial 9 in. of soil was 
composed of blackish-brown humus and loam. For the 
next 14 in. there was a fairly loose sand with broken ‘ grey- 
stone’, and it contained numerous healthy roots of larch 
and oak. Below this to the lowest point reached in digging 
the sand was tenacious, and bound as though with an 
admixture of clay, and contained numerous stones. There 
were few roots in this layer, and many of those which 
T picked out were dead. In fact I estimated that in the 
hard subsoil 60 per cent. of the larch roots and 25 per cent. 
of the oak roots had been killed, though a few of them were 
rotted. This wood—a mixture of larch and oak—was 
54 years old. For comparison I had a similar trench cut 
in a pure oak wood alongside which was 105 years old. 
The soil was here composed of a superficial 3 in. of black 
leaf-mould and 18 in. of a sandy loam with a few stones 
and very many healthy oak roots. At 21 in. (the same 
depth as in the former trench) the sand became much more 
compact, but not nearly so hard as in the younger wood. 
There were a few oak roots, all of which were vigorous. 
The points that chiefly interest us in comparing the two , 
trenches are, firstly, that in the older wood the subsoil is 
much looser and more broken up than in the younger wood, 
and, secondly, that many of the: subsoil roots were dead 
in the younger wood, whereas all were alive in the older 
wood. The cause of death in the former case is almost 
certainly lack of air, for, like all other parts of plants, roots 
must have access to a supply of free oxygen in order to 
maintain their vitality. 
