140 STOMATE8 OF EQUISBTUM. [BOOK i. 



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 intervals 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 macera- 

 tion in water, boiling in strong nitric acid, careful scraping 

 away of the disorganised cellulo- vascular structure, washing, 

 boiling again in nitric acid, and again washing in water, 

 which he considers necessary for the perfect exhibition of the 

 minute structure of the stomates. After a portion of the stem 

 has undergone these processes, the siliceous structures pre- 

 viously 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 opaque, 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 investiga- 

 tion 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 prepara- 

 tion finally assumes a snowy whiteness; it is then placed 

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

 into fragments of a si?e sufficiently small to allow of careful 

 examination by high powers of the microscope. The trans- 

 verse fissure leading externally to the stomatic apparatus is 

 found to have been widened and rendered irregular by the 



