192 Linnaan Society. 



sary for the perfect exhibition of the minute structure of the stomata. 

 After a portion of the stem has undergone these processes, the sili- 

 ceous structures previously observed become much more obvious and 

 distinctly marked. On reversing the preparation so as to obtain a 

 view of its inner surface, the portions corresponding to the rows of 

 tubercles are found to be nearly opake, owing to a compact series of 

 linear masses of siliceous matter combined with some still remaining 

 organic structure. Equidistant from these linear masses are seen the 

 posterior aspects of the stomatic apparatus, each presenting an ovate 

 nipple-like prominence having its longer axis corresponding with 

 that of the stem, and consequently opposed to that of the external 

 fissure, into the base of the conical eminence surrounding which 

 these ovate bodies are fitted. 



Further manipulation is necessary to carry this investigation into 

 the more minute details ; and Dr. Bird has recourse to heat, applied 

 by holding the piece of Equisetum prepared as already described in 

 the flame of a spirit-lamp, in order to get rid of the minute portion 

 of organic matter still remaining in the preparation. After acquiring 

 a red heat, the preparation finally assumes a snowy whiteness ; it is 

 then placed between two slips of glass, which reduce it by breaking 

 into fragments of a size sufficiently small to allow of careful exami- 

 nation by high powers of the microscope. The transverse fissure 

 leading externally to the stomatic apparatus is found to have been 

 widened and rendered irregular by the heat. On bringing this 

 fissure within the focus, it is seen to be replaced by one having its 

 longer axis in the opposite direction, which is derived from the oval 

 figure of the apparatus at its base. Among the fragments may be 

 seen numerous separated specimens of the stomatic apparatus. This 

 is described by Dr. Bird as oval in outline, nearly flat, and measuring 

 in its long diameter -^y^th of an inch. It consists of a frame of silex 

 formed of two pieces, thick at their convexities, thin at their con- 

 cavities, nearly touching above and below, and grasping between 

 them two long and flat structures, fissured (apparently) in a pectinate 

 manner, and tapering from their middle towards either end. In most 

 specimens an opening exists between these structures ; in others 

 they are quite in contact. In some the thinner and laminated por- 

 tions of the frame are perforated by three well-defined apertures, 

 but this is by no means constant. The apparatus thus consists essen- 

 tially of four pieces, viz. two curved frames with their laminae and 

 two linear pectinated structures ; and these are placed at the base of 

 a conical eminence opening by a transverse fissure. By what means 

 it is retained in its position Dr. Bird has not been able satisfactorily 

 to ascertain. 



April 7. — Edward Forster, Esq., V.P., in the Chair. 



Read a " Note on the Generation of Aphides." By George New- 

 port, Esq., F.R.S., Fellow of the Royal College of Surgeons, &c. 



In this note the author states his object to have been the verifica- 

 tion by his own observations of those made by Leeuwenhoek, Bonnet, 

 Reaumur and others, preparatory to attempting hereafter to show 



