NOTE ON THE LARCH DISEASE. 37 



IV. Note on the Larch Disease, By A. W. Borthwick, B.Sc, 

 Hon. Consulting Cryptoganiist to the Society. 



The larch canker disease is caused by a fungus, Dasyscyjyha 

 (Feziza) Willkomniii, Hartig, a wound-parasite, i.e., a fungus 

 which can only effect an entrance into the tissues of the living 

 host through a wound of some description. The disease occurs 

 in the native habitat of the larch in the Alps ; but, unfortunately, 

 is to be found also all over Europe wherever the tree is culti- 

 vated. In its native home (the higher reaches of the Alps) the 

 larch suffers much less from this disease than in places where it 

 has been artificially introduced. The reason for this will be 

 shown later on. 



The fungus belongs to one of the two great divisions of the 

 higher fungi, the Ascomycetes. The main character which 

 distinguishes the Ascoviycetes is the Ascus, a name given to a 

 sporangium of definite size and shape, and containing a definite 

 number of spores. 



The shape of the Ascus is generally club-like, the number of 

 spores usually eight. The cup-like structure which bears the 

 Asci is termed the Ascophore. 



In the body of the fungus two distinct portions may be re- 

 cognised — a reproductive and a vegetative. The vegetative part 

 is composed of fine thread-like strands called hyj)hce, which 

 ramify through the living tissues of the host, and cannot be seen 

 from the outside, nor even when the stem is cut through, with- 

 out the aid of a microscope. The reproductive bodies, 

 Ascophores, are seen as little caps round the margin of the 

 blister, the Asci of which liberate their spores when ripe. The 

 spores will germinate readily in a sufficiently moist atmosphere, 

 but the germ-tube is unable to pierce the unwounded " bark " or 

 " skin " of the host. 



It is quite evident, then, if we could eliminate all agencies 

 which damage the periderm, we would effectually prevent the 

 spread of the disease. What, then, are the agencies which cause 

 damage to the " bark " or periderm 1 These may be included 

 under three heads, namely — animal, physical, and those caused 

 by man. 



