i;i:.\( TKiN UK HOST TO PARASITIC ATTACK. 



to increase in the actual wood elements. This is the case hi 

 twigs <>f silver tir witches' brooms, in young swellings of juniper 

 attacked by Gymnosporangium, and in the thickened twigs of 

 Albizzia resulting fmai Uromycex Tepperianw (Fig. 181). There 

 may I.e. however, a distinctly increased growth of the wood. 

 Thus, witli attacks of Ch/mnosporangium frequenting juniper, 

 especially (!. sdbinae, there is often a marked thickening of 

 uches due to increase in the xylem-elements. Again, one 

 tin.N cankers due to Aecidium datinum, accompanied by stem- 

 sw.-lliii-s witli a diameter twice or three times that of the 

 annual, aad in which the bark and bast form but a thin layer 

 in proportion to the part made up by the wood. Exceptionally 

 -triUin are the iantic woody knots formed on the Japanese 



Pinus dcnsiftora, and P. 

 Thnnbergii affected by Peri- 

 dermiuiii giyanteum (Fig. 

 15). 



Wakker found that mu- 

 cilage canals of Rhamnus 

 Frangula affected by Acci- 





din in were not 

 developed as in 



so well 

 normal 



twigs. 



Eesin-carials are often 

 irregularly formed and ab- 



Kiu. 1".. Wood-swelling on Pinas denstflora, attacked normally multiplied ill CO11- 



;it this jiliL-e by P, riil.ermium tfiganteum. A natural size. " 



(v Tnbeuf phot.) sequence of parasites. The 



(on Piniu /' ; ..'<','/t/-<;astilllargerexamplesmayoccur.) L _ 



resin-canals of the spruce 



were found by Hartig to be so numerous in plants attacked by 

 Agaricus melleus that an abnormal quantity of resin is produced 

 in the wood, and flows from the diseased roots ; hence has 

 arisen the name "resin-glut" or "resin-flux' by which the 

 disease lias long been known. A particularly noticeable flux of 

 r'-sia takes place from pine-bark in presence of Peridcrmium 

 1'ini ; the mycelium grows in the medullary rays and resin- 

 'aaals, causing an excretion of resin from all living parenchyma 

 in the wood, so that both bast and wood become completely 

 impregnated with resin, and thin sections of wood transmit a 

 light. 



