474 PROCEEDINGS OF THE ACADEMY OF [May, 



One of the most frequent results of the action of fungi is that 

 of a stimulus given to cell division. Mention in this connection 

 must be made of the swellings on the stems of silver firs, whose 

 cortical tissues are infested by JEcidium elatinum; the increased 

 growth of the cowberry through the attack of Melaimpora 

 (Calyptospora) Gceppertiana ;^^ of the larch througli the influence of 

 Peziza (Helotium) Willkon.mii.^^ Still more frequently the infested 

 parts are stimulated to display abnormal growths. Flowers and 

 fruits of various species of plants are transformed in a most 

 peculiar manner by fungi belonging to the genus Exoaseus. The 

 disease of the silver fir, however, caused by jEcidiwn {Perkier- 

 mium) elatinmn is the most appropriate one to compare with the 

 canker knobs produced on the white cedar by Gymnosporangiiun 

 hisej)tatuin. The mycelium of this fungus, according to Hartig, is 

 perennial in the cortical and bast tissues of the stem, and even 

 penetrates the cambium and the wood. "With the spread of the 

 mycelium, the swellings or canker spots increase in size, and if 

 present on the stem of a vigorous tree, they may attain to large 

 dimensions. At such places the tissues of the cortex and bast 

 become fissured and dry up here and there, as far as the wood, 

 giving the whole exterior of the swelling a rough, shaggy appear- 

 ance. The swellings resemble much in external character those 

 described by the writer as occurring on the white cedar in New 

 Jersey. Anderson^" describes the changes produced in the cortex 

 of Abies balsamea by Dasyscypha resinaria in the following quota- 

 tion from his paper: " In the bark of the canker, the periderm as 

 well as the primary cortex, and outer layers of the secondary 

 cortex, are very soon cut off by the formation of a neAV phellogen 

 layer. This causes the death of the cut-off layers of the bark, 

 which dry up sooner than in the normal. The resin canals are also 

 cut off and disturbed, and their resin contents begin to diffuse into 

 the surrounding tissues, but mostly collect in the resin vesicles or 

 ' blisters,' which are also formed sooner in the primaiy cortex of 

 the canker than in the normal bark. The resin of the canker 

 vesicles is forced out by the increased pressure on the vesicle, by 

 the shrinkage of the surrounding dead layers of the bark, cut off by 



i"* ITartig, Text-Book of the Diseases of Trees, 1894, p. IGl. 

 ''••PIartig, loc. cit., p. 120. 

 '"Anderson, loc. cit., p. 29. 



