22 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



Soon after the death of the cortical tissues, the cushion-like 

 stromata of the parasite originate in the form of small yellowish- 

 white pustules of the size of a pin-head (Fig. 1 c, Fig. 3 a). In 

 the interior of these stromata, and partly on their surface as well, 

 vermiform passages or roundish cavities are formed, the walls of 



which are covered with in- 

 numerable club-shaped sterig- 

 mata, at whose apex extremely 

 minute cells originate. Whether 

 these organs, which appear to 

 be incapable of germination, are 

 abortive gonidia, or are to be 

 classed with spermatia, remains, 

 in the meantime, undetermined. 

 In this place it is specially im- 

 portant to emphasise the fact 

 that they are incapable of 

 assisting in the distribution of 

 the parasite. 



The small stromata are very 

 readily affected by a dry atmo- 

 sphere and by air-currents, in 

 which they quickly wither and 

 die. They develop only when 

 constantly surrounded by moist 

 air. Under such circumstances 

 they produce the well-known 

 cup-shaped ascocarps (Fig. 3, 

 h h). These possess a hymenium 

 of a tine red colour. The 

 hymenium consists of innum- 

 erable asci surrounded by fila- 

 mentous paraphyses. Eight 

 colourless spores are formed in 

 the interior of each ascus. The 

 fact that the mycelium pene- 



FlG. 3. — A canker-spot ot two years' 

 standing, close to the collar, and 

 hidden by the glass. On the upper 

 portion, which is exposed to air- 

 currents, the stromata are abortive ; 

 but in the lower portion, which has 

 been kept moist, they have devel- 

 oped to form vigorous ascocarps. 



trates even into the wood, and 

 kills it, explains why one or a few small blisters may greatly inter- 

 fere with the growth of the^whole stem. Numerous cup-shaped 

 ascocarps ultimately make their appearance on the dead cortex, 

 and these are met with even when blisters are aVjsent. 



