132 FOREST ENTOMOLOGY. 



In support of the complicated structure of the marble gall the 

 following may l)e quoted — viz. : 



" If a transverse section of a young marble gall, 3 mm. in thickness, 

 be made at the end of June, it will be found, according to Beyerinck, 

 to exhibit the following structure : a larval chamber surrounded by 

 (1) a thin layer of primary nutritive tissue ; (2) a thin layer of cells 

 containing crystals ; (-3) a thin layer of primary starch cells ; (4) the 

 layers of the cambium ring ; (5) a thick layer of large cells, rich in 

 tannin and traversed by vascular bundles ; (6) a layer of small 

 meristematic cells ; (7) colourless hypodermal cells ; (8) epidermis 

 with unicellular hairs containing red pigment in their cell contents." ^ 



The origin and development of vegetable galls, more especially those 

 on the oak, is a subject which has puzzled eminent scientists. It was at 

 first considered by naturalists that the Cynips deposited simultaneously 

 with the egg a drop of irritating fluid, which caused the sap to flow 

 round the egg, and thus a globular form would be the result. In other 

 words, gall-formation was considered the result of chemical action. 

 Darwin adopted this view^, and says : "As the poisonous secretion of 

 insects belonging to various orders has the special power of affecting 

 the growth of various plants ; as a slight difference in the nature of the 

 poison suffices to produce widely different results ; and, lastly, as we 

 know the chemical compounds secreted by plants are eminently liable 

 to be modified by changed conditions of life, — we may believe it 

 possible that various parts of a plant might be modified through the 

 agency of its own altered conditions." In the 'Origin of Species,' 

 p. 572, he says : " When we see the symmetrical and complex out- 

 growths caused by a minute atom of the poison of a gall-insect, we 

 may believe that slight changes in the chemical nature of the sap or 

 blood would lead to extraordinary modifications of structure." In 

 another work he says : " The complex and extraordinary outgrowths 

 which invariably follow from the insertion of a minute drop of poison 

 by* a gall-producing insect show us what singular modifications result 

 in the case of plants from a chemical change in the nature of the sap." ^ 

 This view, on the strength of the great naturalist, was adopted by Sir 

 James Paget, Prof. Riley, and others. From the fact that so many 

 eminent men have been puzzled with this subject, it is obvious that 

 the question is a difficult one. 



^ Adler, p. 163, written bj' Dr Stratton. 



- Animals and Plants under Domestication, p. 9. 



