CHAPTER XXI 

 GALLS 



Galls may be defined as all abnormal tissues produced by the action 

 of animal, or vegetal parasites. The great majority of galls arise either 

 through the growth of cells alone (gall hypertrophy), or by cell division 

 (gall hyperplasia). The number of galls constructed heteroplastically is 

 very large, exceeding the diverse gall hypertrophies. Galls of heteroplastic 

 origin occur in the most diverse kinds of plants and on all organs of these 

 plants. The term gall, or cecidium (cecidia), is applied to those varia- 

 tions in form which are caused by foreign organisms. In the forma- 

 tion of the cecidium, an active participation of the host plant is neces- 

 sary and the biologic connection between the host plant and the gall- 

 producing organism must be considered. Only those cases fall within 

 our purview in which abnormal tissues are produced. 



Considered biologically and etiologically galls form a well-defined 

 group without, however, any one feature common to all. Even when 

 considering only gall hyperplasias, we will find no common characteristics 

 except that a production of heteroplastic tissue is involved in all. This 

 is either extraordinarily simple histologically, showing little or no dififer- 

 entiation, or there are specific differentiations which produce structures 

 entirely distinct from those of normal tissues. The first kind are cata- 

 plasmic galls, and the second kind prosoplasmic. Galls may be clas- 

 sified as to their morphologic characteristics, as well as by their histolo- 

 gic. They may be found on every part of plants, roots, stem, branches, 

 leaves, flowers and fruits and plants capable of producing galls belong- 

 ing to all groups of the plant kingdom. 



The following descriptive terms for galls will serve as a rough clas- 

 sification of their morphologic forms. Connold^ gives an example of 

 each kind. 



As to morphologic character, galls are: axillary, coalescent, con- 

 glomerate, cymbiform, elongated, globose, glossy, gregarious, hirsute 



1 CoNNOLD, Edward T.: British Vegetable Galls, 1901: 24-25. 

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