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, ChamcBcyparis thyoides, 



and Stewart^ has published an 

 account of the anatomy of 

 Gymnosporangium galls and 

 Peridermium galls. 



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 always surrounded with 

 parenchyma illustrate this 

 point. Hartig produced an in- 

 crease of resin ducts in the dis- 

 eased areas of coniferous trees 

 infected by Ar miliaria mellea. 

 Abnormal Bark. — Many 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- 

 cences simultaneously. Wornle found that in weak branches of 

 Juniperus communis a rust fungus, Gymnosporangium davaricBforme, 

 incited the bark to' form woody parenchyma. 



1 Harshberger, John W.: Two Fungous Diseases of the White Cedar. Proc. 

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



2 Stewart, Alban: An Anatomical Study of Gymnosporangium Galls. Amer. 

 Journ. 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.) 



