The Mode of Growth and Classification of Galls 25 



XVII. Scabious = Schizotuura lani- XXII. Rolling and thickening of the 



gera. 



leaf = Ceddomyiapcrsicaria. 



XVIII. Se^ardXe. = Asphondylia pirn- XXIII. Upon the upper surface of 



pemeUte. the leaf = Eriophyes tilia: 



XIX. Sessile = Cecidomyia ulma- lypicus. 



ri(g_ XXIV. Upon the under surface of the 



XX. Solitary = Eurytoma hyali- leaf = Nematiis bellus. 



petinis. XXV. Upon the margins of the leaf 



XXI. Spiny = Rhodites nervoms. = Eriophyes marginatus. 



This list does not include all the different modes of growth, 

 but the few remaining are more of the nature of variations 

 from a given form, and do not convey any idea of individuality, 

 being very irregular in outline and arrangement. E.g. the gall 

 caused by Cecidomyia taxi might be classed as an imbricated 

 gall until a dissection is made of it ; it will then be seen that 

 the leaflets are imbricated, and not the larval chambers, as in 

 Adelges abides, the larva being ensconced in a small cell at 

 the bases of the leaflets. The gall therefore is solitary and 

 unilocular. 



The Classification of Galls. Hitherto there does not appear 

 to have been any special system adopted by English writers 

 for the classification of vegetable galls. There are, however, 

 several ways in which they may be classified, among which 

 are the following : 



I. According to the natural order in the animal world of 

 the creature which causes the growth and issues therefrom. 



II. According to the botanical order of the plant upon 

 which the gall grows. 



III. According to the situation of the gall upon the various 

 organs of the plant. 



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



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

 of two or more larval cells. 



VI. Anton Kerner, in his "Natural History of Plants" 

 (translated from the German by F. W. Oliver, M.A., D.Sc), 

 makes two broad primary groups— simple and compound. By 

 simple is meant when a gall-growth is limited to a single 

 plant-organ. This group is subject to three sub-divisions. 



{a) Felt galls, which are due chiefly to hypertrophied epi- 

 dermal cells growing out into hairy coverings, of various sorts, 

 The majority of these are caused by mites. 



