GALLS 



395 



Witches' Brooms and Stag-head. — ^The branches of the silver fir, the 

 flowers, fruits and portions of stem of various species of plants are trans- 

 formed into witches' brooms, or stag-head by the action of fungi of the 

 genus Exoascus and in the silver fir by Mcidium elatinum. The shoots 



Fig. i6i. — Diagram of a longitudinal section of a cedar twig bearing a small 

 cedar apple in June, a. Epidermis of cedar leaf; b, sclerenchymatous layer; c, fibro- 

 vascular bundle; d, resin gland; e, parenchyma; /, parenchyma of cedar apple; g, 

 fibro-vascular system of cedar apple; h, cortex. {After Reed, H. S., and Crabill, 

 C. H., Techn. Bull, g, Va. Agric. Exper. Stat., May, 1915.) 



are annual instead of perennial and are always sterile and branch out 



into broom-like, or antler-like forms called thunder bushes by some. 



(b) Prosoplasms. — ^Those galls are included, as prosoplasms, which 



do not have arrested tissue differentiations, nor in which callus tissues 



