AGARICUS. 459 



' Eesin-glut.' In the upper parts of the stem, where the cambium 

 and cortex are still sound, the turpentine also flows laterally, 

 by means of the ducts of the medullary rays, from the injured canals 

 towards the cambium and cortex. In the latter this accumulation 

 induces the formation of large resin-blisters. When, during the 

 summer, the cambium is forming a new ring, the plethora of 

 resin has the effect of causing the production of numerous resin- 

 canals, which are usually large and abnormally constructed, and 

 these impart to the wood-ring formed during the year of sick- 

 ness a very striking and characteristic appearance. 



" The mycelium gradually spreads from the cells of the 

 medullary rays and from the resin-ducts into the vascular 

 elements of the wood, where it produces a form of decay which 

 may be termed a variety of white-rot. During the progress of 

 the decomposition from the surface of the stem inwards a certain 

 stage is reached, which is highly favourable to the development 

 of the mycelium. While previously it was simply filiform and 

 furnished with numerous lateral hyphae, it now develops large 

 bladder-like swellings, and at the same time the hyphae change 

 into a kind of large-meshed parenchyma, which, like the tyloses 

 in the vessels of many dicotyledonous trees, completely fills up 

 the lumina of the tracheides. On account of the mycelium 

 assuming a brown colour when in this condition, it makes the 

 portion of diseased wood which it infests appear, to the naked 

 eye, like a black line. As this kind of mycelium soon dies 

 off and is dissolved, being replaced by a delicate filamentous 

 mycelium, it seldom happens that the zone which it occupies 

 exceeds the breadth of three to four tracheids. The walls of 

 the elements of the wood afterwards display a cellulose 

 reaction, and speedily dissolve from the lumen outwards. 



" On account of the trees drying up, after the rhizomorphs 

 have spread from the point of infection on the roots into the 

 stem, and again from the stem into the hitherto sound roots, 

 decomposition of the stem usually ceases before the mycelium 

 has advanced from the alburnum into the duramen. It is only 

 in the stool and roots that decay rapidly spreads throughout 

 the whole of the wood." 



Methods for exterminating this parasite are unknown, beyond 

 removal of diseased plants and collection of sporophores. It 

 would certainly be advisable not to plant young conifers on 



