DAMAGE CAUSED BY PLANTS. 75 



interruption of the canopy of the crops, especially in the case of 

 Spruce, Scots Pine, and Weymouth Pine. Young plants, poles, 

 and trees are suddenly seen to die off, and soon afterwards others 

 in their vicinity follow suit, so that not inconsiderable blanks are 

 often formed in consequence. The snow-white receptacles or spore- 

 producers are then to be noticed externally on the roots, and the 

 fine mycelial threads between the scales of the bark ; whilst the 

 roots, and often the stem itself, for some distance above these are 

 rotten, in consequence of the red-rot produced. The spread of the 

 disease may take place in two ways, either by direct infection from 

 the roots of neighbouring trees that are in contact with those 

 of the diseased stem, or else by the spores being conveyed to other 

 individual plants by animals, especially on the furry coats of mice, 

 voles, and the like. 



Against this latter mode of infection, there are, of course, no 

 means of adopting preventive measures; but against the former 

 Hartig recommends the isolation of infected places by removal of 

 the diseased stems, and the digging of ditches around the infected 

 spots. This proposal has recently been energetically objected to as 

 directly tending to favour in a high degree the further extension 

 of the disease, in consequence of the particularly luxuriant develop- 

 ment of the spore-bearing receptacles of the fungus produced on 

 the diseased roots that are cut through in digging the ditches. 



The common edible Mushroom or Honey-fungus (Agaricus melleus) 

 is also a very common, and in many places a very dangerous, 

 parasite in young crops of conifers, which, however, also occurs 

 extensively as a saprophyte on dead stools and roots of old trees, 

 especially of Beeches. Young plantations of conifers on soil 

 formerly under crops of broad-leaved species, which are now so 

 j frequent in consequence of the deterioration of the soil, due to the 

 I improper treatment of the latter, appear to suffer from this fungus 

 ! to a much greater extent than seems to be the case elsewhere. 

 The blackish-brown mycelial threads, that extend themselves under 

 ; the surface of the soil, push their way into the bark of the roots 

 with which they happen to come in contact, and develop them- 

 selves under it as long, white, ribbon -like filaments, ultimately 

 causing the death of both young plants and old trees. Infected 

 plants exhibit a strong outflow of resin at the base of the stem 

 which penetrates and cements the soil round the foot of the tree. 

 , Before the true explanation was known, this gave rise to the belief 



