1912] Morphology and Biology of Insect Galls 351 



parenchyma just beneath the small-celled epidermis. This outside pro- 

 tective sheath gradually passes into the parenchyma zone by the con- 

 stituent cell walls becoming thinner. The large size of the cells in the 

 parenchyma layer marks them out from the rounder and smaller cells of 

 the nutritive zone. 



Below the depressed area, mentioned in the macroscopic description, 

 is a small patch of sclerenchymatous cells. In position and character 

 these cells appear to be homologous to the groups of cells that block the 

 canals in different species of Andricus. Only the mature stage of this 

 gall was examined, but in all probability the depression at the top is the 

 remains of a canal that connected the gall cavity with the outside in the 

 early stages of development. A part of the normal epidermis of the leaf 

 was held fast by the closing of this canal, and when the gall was forced 

 out beyond the leaf tissues a small patch of the epidermis of the leaf was 

 carried out on it. This persists in the later stages of development as the 

 scale of tissue in the depression. 



Rhodites gracilis Ashm. 

 Host Rosa hlanda Ait. 



A thin -walled, monothalamous gall produced from the mesophyll of 

 the under surface of the leaf of the host. Occurs singly or in clusters on 

 the leaflets. 



It is irregularly spherical with a broadened top, in the centre of 

 which is the same shallow depression and scale-like patch found in R. 

 ignotus O.S. Numerous ridges radiate out from the point of attachment 

 of the gall, pass up its sides and project as short blunt tubercles around 

 the top. 



Dimensions: — Diameter 5-6 mm. 



This species resembles closely R. bicolor Harr. in anatomical struc- 

 ture. It presents little differentiation of tissue. The protective sheath 

 is not present, and the parenchyma and nutritive zones are marked out 

 from each other only by the cells of the latter being slightly smaller and 

 more circular in outline. The observations on the preceding species con- 

 cerning the depression at the summit of the gall and the discussion of 

 them also apply to this species. 



Rhodites nebulosus Bass. 

 Host Rosa hlanda Ait. 



This species, as the preceding, is monothalamous and thin-walled. It 

 also originates from the mesophyll of the leaf of the host. It occurs 

 usually in dense clusters deforming the entire leaflet. 



The gall is spherical in form, bearing at the summit the depressed 

 area and scale-like patch characteristic of the two preceding species. 



