The Mode of Growth and Classification of Galls 27 



While neither adapting itself to every requirement, nor 

 satisfying each detail, a classification based upon the position 

 the gall occupies upon the main divisions or organs of a plant 

 appears to fulfil nearly all the necessary qualifications in as 

 comprehensive a manner as possible, and to provide a basis 

 upon which the gallist can construct any more elaborate system 

 which may be thought desirable. 



IV. According to the mode of growth of the gall. 

 Although this would not be so extensive as No. II., a 



classification based upon the twenty-five or more different 

 modes of growth, is too wide in its scope to possess the 

 advantages offered by one of a more concise character. Some 

 galls which during their earliest stages of growth are glabrous 

 become pubescent before attaining maturity. Some which are 

 sessile while growing ultimately assume a pedunculated form. 

 Others which on one portion of a leaf will be separate, are 

 gregarious and coalescent on another part of the same leaf. 

 In fact, no reliability can be placed upon the features, which 

 are quite of a secondary character. 



V. Whether the gall consists of one larval cell only, or of 

 two or more larval cells. 



Most descriptions of galls have been based upon the number 

 of the cells or larval chambers. The terms which have thus 

 been employed are unilocular, or monothalamous ; and plurilo- 

 cular, or polythalamous. 



A unilocular gall consists of a definitely formed separate 

 cell, solitary or gregarious, embedded or not embedded in the 

 tissue of the plant, and irrespective of its size, shape, or the 

 position which it occupies on the plant. 



A plurilocular gall consists of two or more cells, coalescent 

 or conglomerated, embedded or not embedded in the tissue of 

 plant, and irrespective of their size, shape, or the position which 

 they occupy on the plant. 



There are several objections to a definite classification 

 according to these terms. 



The larvje of some species do not inhabit a definitely 

 constructed cell, yet they produce gall-formations. Many galls 

 which, when occupied by the rightful larva, are unilocular, 

 become plurilocular when the larva or larva; of parasites also 

 inhabit the gall. Other galls which normally consist of a single 



