SECT. V. THE LEAF. 283 



of the leaf, by making- a small perforation on the 

 under surface.* So also various other excrescences 

 are generated on the leaves of Oaks of other species. 

 If the leaves of Quercus Robur, or the common 

 Oak of this country, are inspected in the beginning 

 of summer they will often be found to be disfigured 

 by a small purple coloured excrescence, about the 

 size of a Whortle-berry, partly imbedded in the 

 parenchyma, but chiefly swelling above the surface. 

 Having cut open one of these excrescences in the 

 month of May I found it to consist of a white and 

 glary fluid. And on inspecting some others in the 

 month of June following, nothing now remained 

 but the shrunk and withered bag in which the fluid 

 was contained. I had not an opportunity of ob- 

 serving the intermediate stages ; but it had un- 

 doubtedly been the nidus of some species of 

 4nsect. 



On the leaf of SalLv alba there is often also to be Gall* of 

 found about the month of June an oblong and i *v-ieaf? 

 glandular tumor, sometimes at the apex, and some- 

 times about the middle region, of about the size of 

 a Pea, assuming a reddish appearance with age, 

 and a villous exterior, which if cut open is found to 

 envelope a single maggot. 



On the leaf of the Clinopodium vulgar e I have And cii 



also found in the month of June a sort of gall or 



excrescence of about the size of a Kidney Bean, 



but larger at the one end, of a deep purple, and 



* Withering, vol.. ii. p. 388. 



