ON THE DISEASE OF THE LARCH. 143 



on this estate on the banks of the lakes, where the soil consists 

 of a thin, mixed, peaty loam, resting on sandy gi*avel, there are 

 a number of fine old trees, and though the water often runs 

 over their roots to within a foot of the level on which they grow, 

 they are still, to all appearance, sound and full of vigour. The 

 situation may be on hill-sides or on the bottom of ravines, other 

 things being equal. As to exposure, the tree is very hardy, and 

 will rear its head where the beech gives way ; nevertheless, it 

 ought to be planted where the natural configuration of the country 

 screens it from the prevailing winds. 



Blister, or Cancer, or Canker. — The appearance of this disease is 

 too well known to all foresters, and requires no description here. 

 Cancer is caused by anything that suddenly checks the flow of sap 

 to the small lateral branches. It invariably begins in one-year- 

 old wood, and in most cases at the junction of the branch with the 

 main stem. It seldom breaks out in the latter, but when it does 

 it is always at a bud. In young plantations it affects first the most 

 luxuriant grown trees when in warm, damp situations ; and in all 

 woods it affects most those trees already attacked with heart-rot, 

 since the flow of sap presses to the outside vessels by being unable 

 to circulate in the centre of the tree. Generally speaking, the 

 disease usually affects the same side of the tree, but in some situa- 

 tions there are blotches to be found all over it. These appear- 

 ances point clearly to the cause of the disease. 



The flow of sap is checked by intense cold, such as early autumn 

 frosts, which injure the buds and wood before they are matured, 

 and also by late spring frosts after the buds are expanded. 

 The main stem being thicker, is not so much affected by the frost 

 as to prevent the flow of sap upwards through the trunk, but the 

 congealed laterals check its passage through them till thaw takes 

 place. Very often this suddenly occurs by the heat of the sun, 

 the result being an increased pressure at the junction of the branch 

 with the stem, which bursts many of the sap-vessels arranged 

 round the base of the branch, and causes the sap to flow out at the 

 rupture, producing an irregular growth, and leaving a gummy, 

 black, resinous substance on the tree. Eventually the branch 

 dies very often the first year after the rupture takes place ; and if 

 there are many of these ruptures, the tree presents a very sickly 

 appearance, and in a few years dies off above the rupture. The 

 wounds invariably occur on the side exposed to the prevailing 

 winds, and generally more about the outside of plantations, 



