ROBERT HARTIG ON THE LARCH DISEASE. 



21 



during the first year dries up and appears as a depression, 

 especially after growth in thickness has been resumed by the 

 healthy part of the tree (Fig. 1). 



In summer the growth of the mycelium ceases, and an un- 

 usually broad layer of cork is formed for the protection of the 

 tree along the boundary -between the sound and diseased tissues. 

 These layers of cork (Fig. 2, b b) which form between the dead 

 and living tissues induce external rupturing of the cortex at 

 points along the boundary of the canker-spot (Fig. 3), the result 

 being that turpentine flows from 

 the interior of the tree. Year 

 by year the canker-spot enlarges 

 along its whole periphery, rather 

 more rapidly, however, longi- 

 tudinally than horizontally, and 

 it is probably the vital activity 

 of the cortical tissues which in 

 summer causes a temporary in- 

 terruption to the progress of 

 the parasite. In autumn the 

 mycelium again succeeds in 

 entering the living bast, either 

 through the cambium region or 

 by way of the wood, so that, as 

 a matter of fact, th« layer of 

 cork is only of slight service. 

 In proportion as the passage of 

 the plastic siibstances is con- 

 fined to one hide of the tree, 

 growth of the wood and bast is 

 stimulated at that part (Fig. 

 2). Thus the conflict between 

 parasite and host-plant may re- 

 main long undecided, and in the Tyrol I found larches still alive 

 with blisters of a hundred years' standing. 



Should the parasite advance relatively quickly, and, at the 

 same time, should the growth of the tree at the affected part be 

 slow, then the canker-spot soon embraces the whole stem or 

 branch (Fig. 2), and the tr«-e dies above this spot. 



By artificial mycelial infection one may, almost without fail, 

 produce a blister on any part of a sound larch. 



Fig. 2. — Cross section of a well- 

 grown larch which has been at- 

 tacked by P. Willkommii. Infec- 

 tion had occurred ten years 

 previously at the dwarf shoot, a. 

 Each year the mycelium advances 

 in opposite dkections, in spite of 

 the fact that a layer of cork, 6 h, 

 is formed at the beginning of each 

 growing season along the boundary 

 of the living tissue. In the im- 

 mediately preceding year a very 

 small quantity of wood had been 

 formed. 



