35° 



GENERAL PLANT PATHOLOGY 



red cedar by Gymnosporangmm juniperi-virginianm. The crown galls, 

 or possible vegetal cancers, are another illustration of such excres- 

 cences, while malformations are represented by peach leaf curl and 

 the witches' brooms on trees. 



12. Exudations.— The formation of slimy substances, which flow 

 from trees and plants, the diseased conditions known as bacteriosis, 

 •rummosis' and resinosis, illustrate the character of the exudations from 



Fig. 139. — Burl, or enlarged base of an oak tree in. the forest on Gardiner's Island, 

 New York, July 17, 1915. 



plants under abnormal conditions. The production of clear amber- 

 colored secretions, which accumulate on the surface of the diseased parts, 

 is known as gummosis and is seen in cherries, apricots, almonds and 

 many other trees. It follows wounds or the attack of fungi. The 

 same condition in coniferous trees is known as resinosis and in a few 

 trees it is of economic interest because, as in the spruce, the exudation of 



' Wolf, Frkdehick A.: Gummosis. The Plant World, 15: 49-59, March, 1912. 

 Butler, O.; A Study on Gummosis of Pnimis and Cilriis. Annals of Botany, 

 25: 107-153, 1910. 



