496 PROCEEDINGS OF THE ACADEMY OF [May, 



16. Tlie retardation of growth, witli the persistence of the win- 

 ter's cold in the bog, also exerts an appreciable influence on the 

 growth of the parasitic fungi, which cause the canker-like swellings 

 on the white cedar. 



17. It is assumed that the perennial habit and slow growth of 

 the mycelia ai'e direct expressions of the inhibitory effect of the 

 cold environment. 



18. In considering the pathological transformations, a compari- 

 son is instituted with the disease produced by Dixsyscypha resinaria 

 in Abies balsamea. 



19. By means of a table it is shown that the number of tracheids 

 in a swelling produced by one of the fungi is vastly greater than in 

 a normal stem of the same age. 



20. The increased activity of the phellogen is also a marked 

 feature of the disease due to Gymnosporangium hiseptatum. 



21. Several additional well-marked layers of cork are laid down 

 as a result of this activity of the cork cambium. 



22. As the disease progresses these cork layers begin to slough 

 off. 



23. The formation of the excrescences through the death of the 

 cambium in part, and the attempt made on the part of the host to 

 repair the damage are minutely described. 



24. Pathological changes in the wood due to G. hiseptatum result 

 in the plugging of the tracheids and the final cracking of the sap- 

 wood when the parasitic attack has been long maintained. 



25. The number of plugged tracheids is shown by an enumera- 

 tion to be extremely variable in the several annual rings of 

 wood. 



26. The material filling the plugged tracheids in the disease 

 caused by G. biseptatwn is supposed to be fungus gamboge, from a 

 number of chemical reactions obtained for the purpose of deciding 

 this question. 



27. Resin is also present in the most diseased areas, as deter- 

 mined by the copper acetate (llnverdorben-Franchimont) reaction. 



28. The mycelium of G. bisejMtum is desci'ibed as a loose net. 

 The hyphse penetrate the wood, cambium and phloem cells, spread- 

 ing longitudinally and horizontally. 



