Ixx Journal of Proceedings. 



especially. These he thought partook of a vegetative or fungoid, para- 

 sitical nature, and were clearly distinct in their origin and development 

 from true galls produced by insects. 



]Mr. Letchford called attention to the very remarkable chemical sub- 

 stances found in abundance in the tissues of many galls. These 

 substances appeared to exist in the sap of the trees, but became concen- 

 trated in the galls, and seemed to be a necessary concomitant of tlieir 

 growth. 



Mr. Henry Walker gave some details as to the morphological structure 

 of galls, and alluded to the appearance of the Devonshire or " Marble- 

 gall " {Cijnips Kollari), near London, within living memory. Many years 

 ago the late Frederick Smith put a large quantity of these galls into 

 Highgate Wood, and he thought it was possible that the rapid spread of 

 the marble-gall might have had some connection with that circumstance. 

 Mr. Walker also called attention to the bearing of the very remarkable 

 observations of Dr. Adler as to the existence of di-morphism in galls 

 upon the current theories of evolution. 



Mr. Meldola stated that there had always appeared to him one difficulty 

 in connection with the mechanical theory of galls which he would be glad 

 to see explained. He did not wish his remarks to be considered in 

 any way critical, but he could not help feeling that there was an objection 

 which Mr. Fitch would perhaps throw some light upon. In accordance 

 with what he would call the purely mechanical theory of galls these 

 growths were caused by the presence of the egg of the insect laid in the 

 leaf-tissue or other part of the plant, and acting as a local irritant. He 

 could easily understand how on this ^dew differently formed galls might 

 result from the irritating action of eggs laid in different parts of the 

 plant, but he could not see how on this theory it was possible to account 

 for the fact that on the leaves of the same plant a large number of insects 

 could each give rise to a differently formed gall. It had been proved that 

 the egg continued to grow for some time within the gall, but this did not 

 appear to him sufficient to explain the fact mentioned. A different form 

 of egg, and a different rate of growth for each species, was assumed, 

 but this was so far only an assumption ; experimental and observational 

 proofs were required in order to demonstrate conclusively that there 

 existed a connection between the form and rate of growth of the egg 

 and the form of the gall. As to the points raised by Mr. Walker, 

 Mr. Meldola said that he had lately been working at them, and hoped 

 to address some remarks upon the subject to the Club at the Annual 

 ^Meeting. 



In reply, Mr. Fitch stated, with reference to Dr. Pearce's remarks, 

 that Sir .Tames Paget, in making his comparisons, had expressly noted 

 the great contrasts between the pathology of animals and plants. 

 From his own point of view also it was by no means intended to 

 institute a comparison between the special viruses which we know are 

 capable of being artiticially introduced into the human body, or with 



