GALLS 393 



often only moderately developed. Wakker describes the disappear- 

 ance of the coUenchyma in the stalks of Vaccinium vitis-idaa infected 

 with Exobasidium. Hyperplastic excrescences may be found by the 

 pith as in branches of Clematis attacked by Mcidium Englerianum. 



Secondary Tis^es. — Under this head will be considered the products 

 of the cambium. The formation of galls may be due to the division of 

 the living derivatives of the already-formed annual ring, or as in wound- 

 wood, its own cells are used in the production of the cataplasmatic tis- 

 sue. The wood and bark swellings formed by the attack of animals and 

 fungi may be clustered or knob-like and resemble the frost-induced 

 cankers or even the witches' brooms. 



Abnormal wood found in many woody galls is induced by many 

 fungi belonging to the genera Dasyscypha, Gymnosporangium and Peri- 

 dermium, by insects, and by parasitic flowering plants. A character- 

 istic feature of such gaUs is the abnormal increase in the parenchyma, 

 produced by the division of the cambial derivatives, which give rise to 

 group of parenchymatous cells. Sometimes the cambial rays are 

 broadened, so that extensive continuous masses of parenchymatous 

 wood are produced. The same kind of tissue formation is seen in an 

 examination of mycocecidia and zoocecidia. The mycocecidia may be 

 illustrated by a brief consideration of the spindle-like, or ball-like, 

 woody galls induced on different species of Juniperus by forms of the 

 genus of rust fungi, Gymnosporangium. In the diseased wood, the 

 difference between the spring and autumn wood is scarcely recognizable, 

 and the parenchyma occupies a relatively broad space. The cambial 

 rays in the parts of the branches infected by Gymnosporangium clavar- 

 iesforme, instead of being only two to ten cells deep, are often ten to sixty 

 cells deep and at least three cells broad. The woody gall of Gymnospor- 

 angium juniperi-virginiana shows still broader cambial rays, when 

 viewed in tangential longitudinal section. According to the investi- 

 gations of Reed and Crabill,' the cedar apple gall is a modification of 

 the leaf of the red cedar (Fig. i6o). The cedar leaf parenchyma makes 

 up the greater portion of the cedar apple with the fungous hyphae in 

 the intercellular spaces of the parenchyma cells. 



The fibrovascular system of the gall is a modified continuation of the 



1 Reed, Howard S. and Crabill, C. H.: The Cedar Rust Disease of Apples 

 Caused by Gymnosporangium Junipcri-Virginiance. Technical Bull, g, Va. Agric. 

 Exper. Sta., May, 1915. 



