394 



GENERAL PLANT PATHOLOGY 



fibrovascular system of the cedar leaf (Fig. i6i). From, or near the 

 base of the cedar apple, where the vascular elements are much con- 

 torted, arise many branches, which extend radially almost to the cortex. 

 Harshberger* has investigated the galls produced by two species of 

 Gymnosporangium on the coastal white cedar, Chanuecyparis thyoides, 



and Stewart^ has published an 

 account of the anatomy of 

 Gymnosporangium galls and 

 Peridermium gaUs. 



There may be an over-pro- 

 duction of the wood paren- 

 chyma and the parenchymatous 

 elements may divide without 

 abnormal widening of the 

 annual ring. The production 

 of abnormal resin canals which 

 are alwa}^ surrounded with 

 parenchyma illustrate this 

 point. Hartig produced an in- 

 crease of resin ducts in the dis- 

 eased areas of coniferous trees 

 infected by Armillaria mellea. 

 A bnormal Bark. — Manj- gall 

 formations exist where exten- 

 sive bark excrescences are pro- 

 duced whereby there is an ab- 

 normal formation of paren- 

 chyma. An examination of 

 the galls due to species of 

 Gymnosporangium shows that 

 the bark and wood form excres- 

 simultaneoush-. Womie found that in weak branches of 

 Juniperus communis a rust fungus, Gymnosporangium clavariaforme , 

 incited the bark to form woody parenchyma. 



> Haxshberger, John W.: Two Fungous Diseases of the WTiite Cedar. Proc. 

 .\cad. Nat. Sci., Phila., 1902: 461-504, with 2 plates. 



= Stewart, Albax: An Anatomical Study of Gymnosporangium Galls. Amer. 

 Joum. Bot, ii: 402-417, October, 1915; Notes on the Anatomy of Peridermium 

 Galls, do, iii: 12-22, January, 1916. 



Fig. 160. — Unopened cedar apples on red 

 cedar. Juniperus virginiana. (After Jones 

 and Bartholomew, Bull. 257, Agric. Exper. Stat. 

 Univ. Wise. July, 1915.) 



cences 



