1S4G.] Linnean Society. 291 



the siliceous masses on its surface and their action on polarized light. 

 He then proceeds to describe minutely the structure of this siliceous 

 armour. The fourteen longitudinal ridges on each joint of the stem 

 are each furnished with two parallel rows of siliceous tubercles, 

 having the lustre and general appearance of glass beads ; and along 

 the margins of each ridge are numerous longitudinal wavy lines, 

 which fill up the inter^^als between the lateral aspects of the ridges 

 and the centres of the contiguous furrows. In the depressions of 

 these furrows is seen a double vertical series of oval projections, 

 arranged in pairs, each furnished with an oval fissure, having its 

 longer axis placed transversely ; these fissures lead to the complex 

 stomatic apparatus. 



Dr. Bird details the manipulations, consisting of maceration in 

 water, boiling in strong nitric acid, careful scraping away of the 

 disorganized cellulo-vascular structure, washing, boiling again in 

 nitric acid, and again washing in water, which he considers neces- 

 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 



