118 HEART-ROT 



from otlier woods. A rootstock sent nie from Tiiiteru 

 showed the .same phenomenon, and a wind-blown lareh on 

 the Endsleigh estate had been I'ottcd solely through its 

 tai)-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 tliis 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 blacldsli -brown humus and loam. For the 

 next 14 in. there was a fairly loose sand Avith broken ' grey- 

 stone ', and it contained numerous health}^ 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 

 I 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 1 had a similar trench cut 

 in a ])ure 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 w liich A\ere vigorous. 



Tlic i)oints that chiefly interest us in comparing the two 

 trenches are, firstly, that in the older wood the subsoil is 

 much looser and moie broken up than in the younger wood, 

 and, secondly, that many of the subsoil roots wc^jc dead 

 in the younger wood, whereas all weie alive in the older 

 wood. The cause t)f death in the former case is almost 

 certainly lack of aii-, foi', like all other parts of plants, roots 

 nuist have access to a supjjly of free oxygen in order to 

 maintain their vitality. 



