THE DISEASES OF CONIFERS. 



143 



which favour certain enemies of the Larch at the very time that 

 they are acting prejudicially to that tree itself. 



I have great confidence, therefore, in the well-thought-out 

 view, first put forward, I believe, by one of the most distinguished 

 and able of modern investigators — Professor Robert Hartig, of 

 Munich — that the appalling liability of the Larch to disease at 

 low altitudes, and in climates which are too moist and variable 

 during the spring and early summer, is due to the co-operation 

 between the factors of the inorganic environment and the 

 directly injurious action of its living enemies. 



The Larch suffers severely from several fungus diseases — 

 Agaricus melleus, Tmmetes Pini, Folyporus sulphureics, and 

 others being among them ; but all other forms have sunk into 

 insignificance beneath the overwhelming importance of the 

 " Larch-disease," or " Larch-canker," due to the parasitism of 

 a minute discomycetous fungus known variously as Peziza 

 Wilkommii, Laclinella calycina, Dasyscyi^ha calycina, &c.* 



The main facts t which are of importance to you are, that this 

 Peziza develops from its spores a mycelium which, when once 

 it has established a hold in the inner cortex of a branch of the 

 Larch, can go on growing and extending into the cambium ; 

 this it kills, destroying a larger area year by year, and producing 

 the so-called "canker " patch, which is simply a shrivelled mass 

 of dead tissues impregnated with exuded turpentine or resin. If 

 the dead patch extends all round the branch or stem, all the 

 parts above may die off, partly because, the cambium being 

 destroyed, there is no more wood developed at that region to 

 carry up the water supplies to the leaves, and partly because the 

 resin blocks up the wood which it permeates. 



To understand how it is that the Larch-fungus spreads so 

 rapidly and with such dire effect in Great Britain, it is necessary 

 to note some peculiarities not always properly appreciated. 



Peziza Wilkommii, like other fungi, requires merely water, 

 oxygen, and a suitable (not very high) temperature for the ger- 

 mination of its spores ; given these, the germinal hyph^e are 

 developed anywhere. The mere germinatioii of a spore may, 

 therefore, take place on any damp surface exposed to the air — 



* For the synonyms consult Phillips, " Brit. Discomycetes," p. 241, 

 and Saccardo. 



f An illustrated detailed account of this and similar diseases is given in 

 *' Timber and some of its Diseases " (Macmillan & Co.). 



