1 8 The Scottish Naturalist. 



present. In the eggs were embryos almost ready to emerge, so 

 well formed that they moved actively within the transparent 

 shell. They are three or four times as long as the oval eggs. 

 In size the creatures approach very closely to those from the 

 gall on Elymus described below. Usually only one gall is 

 found on each leaf, but occasionally two may be situated side 

 by side, separated by the midrib, or both may occur on the same 

 side, but one a little way farther from the base of the leaf than 

 the other. I have seen three galls on a leaf. Magnus (' Botan. 

 Zeitung,' 1875, P- 579; a °d 1876, p. 586) has described similar 

 galls found by him on leaves of Festuca ovina, L., and of Agrostis 

 canina, L. ; and AnguillulcE. have been found to form galls on the 

 inflorescence of Agrostis sylvatica, Huds., of Phleum Boehmeri, 

 and of Ph. prataise^ and have long been known (under the 

 name of Vibrio tritici) to cause " ear cockles " or galls in the 

 ovary of wheat, and, less frequently, of oats and of rye. 



Elymus arenarius, L. — On this coast - frequenting grass I 



have found, near Aberdeen, galls on the fine rootlets pushed out 



from the rhizomes through the sand. They usually occur at the 



tip of the rootlet as a nearly round or oval swelling affecting its 



whole circumference, and tipped with a small knob, — the only- 



slightly- affected extreme end of the root. They vary in size 



from -g 1 ^ to oV mcn m diameter ; but, though so small, are 



easily distinguished, as the rootlets are only about t £q- inch 



thick. Some galls affect the rootlet nearer its base, causing a 



tapering swelling, which may reach ^ x T V inch in size. A 



transverse section of a normal rootlet is found to present a 



central fibro-vascular bundle of rather small thin-walled cells and 



vessels, the whole surrounded by two layers of cells with the 



cell-walls markedly thicker, especially on the inner side of the 



cells. Between these layers and the epidermis lie four or five 



layers (forming the cortex) of regular thin-walled cells, those to 



the inside smallest, those in the middle much larger than the 



inner and slightly larger than the outer cells. These contain 



usually some protoplasm, seldom filling half the cell, in which 



lies a nucleus by no means conspicuous. Outside of all is the 



epidermis, composed of a single layer of cells, distinguished from 



those below them chiefly by being empty, and by. giving off 



root-hairs. 



Comparing the structure of a gall with this, we find the follow- 

 ing differences : The root-hairs are absent, as might be antici- 

 pated from the position of the galls ; the epidermis has the cells 



