210 DISEASES OF TREES 



sowing the spores in a decoction of plums. The pathological 

 symptoms can only be explained in the light of the peculiar 

 organization of the mycelial growth that lives in the cortical 

 tissues. The apex of the rhizomorphs (Fig. 130) consists of 

 delicate pseudo-parenchyma, which, elongating by the division 

 and growth of the cells, produces delicate hyphae on the inside 

 at a certain distance from the point, whereby a felted tissue, 

 called the medulla, is produced in the interior. The outer parts 

 of the pseudo-parenchyma (Fig. 130, c\ on the other hand, 

 coalesce to form the so-called rind (Fig. 131, d), which when 

 young gives off numerous delicate hyphae, and these, taking 

 advantage of the medullary rays, penetrate the wood, and 

 especially the resin-ducts, should such be present. In the wood 

 the growth is upwards. This filamentous mycelium, which 

 progresses much more rapidly in the interior of the wood 

 than the rhizomorphs which grow in the cortex, completely 

 destroys the parenchyma that exists in the neighbourhood of 

 the resin-ducts, and to all appearance this is accompanied 

 by a partial conversion of the cell-contents and the cell-walls 

 into turpentine (Fig. 131). The turpentine sinks down under 

 its own weight, and in the collar, where the cortex is 

 withered, having been killed by the rhizomorphs, it streams 

 outwards, pouring partly in between the wood and the cortex, 

 and partly into the surrounding soil at places where the cortex 

 has ruptured owing to drying. On this account the disease was 

 formerly called " Resin-flux " or " Resin-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 unusually 

 large and abnormally constructed, and these impart to the wood- 

 ring formed during the year of sickness 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 



