204 THE NEW FORESTRY. 



regarding the cause of its development and virulence under 

 various conditions are correct. There seems to be no doubt 

 now that the disease is caused primarily by a fungus, Peziza 

 wilkommii, because experts claim to have proved that the 

 disease can be produced anywhere by innoculation. Granting 

 this, Hartig's theory of the spread of disease throughout 

 Europe is probably the right one. This theory, put shortly, 

 is, first, that the disease has always existed, but not to a des- 

 tructive extent, in the native habitat of the larch in high 

 Alpine regions ; second, that when the tree was first distri- 

 buted throughout Germany, Britain and elsewhere, the disease 

 (not being propagated by the seeds) was left behind in its 

 native habitat and the trees distributed flourished to perfec- 

 tion ; third, that after larch woods of all sizes had been 

 established, from the foot of the Alps to the coasts of the 

 North Sea and the Baltic, affording a continuous line of 

 communication, the fungus spread downwards from the Alps 

 to find everywhere the most favourable conditions for its 

 development. These consisted of dense pure woods and 

 groups, moist, stagnant air, and wounds from various causes 

 at which the disease entered. Preventive measures, it is 

 held, should consist in planting the tree, not in pure woods, 

 but in small proportion in mixed woods, and in open airy 

 situations (see Hartig's " Diseases of Trees " the larch). 

 Hartig, arguing that fungi require much moisture in the air to 

 assist their development, thinks that the larch fungus is almost 

 certain to be worst in low-lying, damp situations, an opinion 

 shared by some foresters, but open to doubt. It is known, 

 for example, that the conditons as regards rainfall, moisture, 

 and sunlight vary greatly in this country, and according to 

 Hartig's theory we would expect the disease to be most 

 virulent in wet districts and situations ; but that is not the 

 case, for in very dry localities the disease is found in its 

 worst form, and not always bad in wet ones. We have seen 

 many diseased plantations in England and Scotland, and the 

 very worst case we ever saw was in Norfolk, near the mouth 

 of the Wash, where the rainfall is about the lowest in England, 

 the situation dry, and the soil favourable, as indicated by the 

 health of older larch crops at the same place. A plantation 

 about seven years of age, that had grown in that time to a 

 height of fifteen feet or more, was a mass of disease. The 

 stem of every tree was almost covered with blisters, which 

 also extended to the side branches up almost to the base of 

 the current year's growth. On branches four-and-a-half feet 



