1902.] NATURAL SCIENCES OF PHILADELPHIA. 497 



29. The hyphiB in growing from traclieid to tracheid take advan- 

 tage of the bordered pits, the middle lanielhi of which disappears 

 by ferment action. 



30. The relation of the hyphjc to the host cells is carefully 

 described. 



31. The mycelium of G. Elllsii is more copious than that of 

 G. biseptatum. It also grows through the cortex, bast and wood. 



32. The hyphse of this fungus are characterized by the veutri- 

 cose swellings produced, and by the fact that they grow into the 

 intercellular spaces of the brown patches of diseased tissue formed 

 in the W(jod. 



33. The hyphfe of G. Ellisii grow through the lumen of the 

 tracheids and from tracheid to tracheid by means of the bordered 

 pits, much as in the other fungus described. 



34. The distribution of the tracheids containing hyphse is pre- 

 sented in tabular form. 



35. The pathological conditions induced by G. Ellisii are more 

 severe at first than those caused by G. biseptatum. 



36. Patches of diseased tissue are found in the stems of white 

 cedar as brown spots of a wedge shape. These brown areas become 

 more or less confluent until they may involve the circumference of 

 the stem. Into these brown patches the hyphre grow. 



37. An enumeration of the tracheids in the diseased branches is 

 also presented in tabular form, as a means of comparing the size of 

 noi-mal and diseased stems. 



38. The belief is expressed, in conclusion, that the fungi cause 

 marked metabolic changes in the stem, accompanied by the accumu- 

 lation of resins and other substances, products of increased cell 

 activity. 



39. A tabular comparison of the several species of the genus 

 Gymnosporangium is presented to show the relationship of the 

 fungi studied to other species of wide distribution. 



40. The bibliography details the papers consulted in the prepara- 

 tion of this paper by the writer. 



