BULLETIN OF THE BUSSEY INSTITUTION. 173 
inet-makers, and comb-makers, but was in demand in the kitchen also, 
for scouring pewter and wooden ware.* 
It is not merely the absolute amount of silica in the equisetum plants 
that must be considered, but the position of the silica at or near the 
external surface of the plant, and the form in which the silica has been 
deposited in the plant-cells.| According to Sachs,t the cells of the 
epidermis or external coating of the equisetum plant, even those which 
form the breathing-pores, are very much silicified upon their outer 
walls; and there are very often on the outer surfaces of the cells protu- 
berances of various forms, which are likewise very strongly silicified. 
These protuberances are in the forms of granules, bunches, rosettes, 
rings, and tongues, of transverse bands, and of teeth or spines. Upon 
the cells of the breathing-pores, they take the form of bands or ridges 
perpendicular to the orifice of the pore. 
So too, according to H. Rose,§ when equisetum stalks are calcined, 
there remains a highly silicious ash, which is seen under the micro- 
scope to retain perfectly the form of the original unburned stem. 
The following list comprises the amounts of ash and of silica in the 
ash that have been found in equisetum plants by various observers : — 
Braconnot || found in dried sterile stems of Hgwisetum arvense 
13.84% of crude ash, and in this ash he found 45.97% of silica; in 
E. fluviatile he found 23.61 % of ash, and, in the ash, 50.83% of silica; 
in £. limosum he found 15.50% of ash, and in the ash 41.94% of 
silica; in Hguisetwm hyemale he found 11.81% of ash,{[ and, in the 
ash, 74.09% of silica. These numbers .correspond with the following 
percentages of silica in the dry plants themselves; viz., 6.388% of silica 
in £. arvense, 12% in EL. fluviatile, 6.5% in E. limosum, and 8.75% 
in L. hyemale. 
Witting ** found in fresh sterile stalks of H. arvense 78.45% of 
water and 4.07% of crude ash (7.e., 18.89% of ash in the plant dried 
- * Loudon “ Encyclopedia of Plants.” Compare Braconnot, “Annales de 
Chimie et de Physique,” 1828, 39. pp. 5, 22. 
+ Compare Johnson’s “ How Crops Grow,” New York, 1868, p. 185. 
t “Traité de Botanique,” Paris, 1874, p. 493. 
§ Poggendorff’s ‘ Annalen,” 1849, 76. 559. 
| ‘ Annales de Chimie et de Physique,” 1828, 39. 24. 
J Hawes (“ American Journal of Science,” 1874, 7. 585) found 11.70% and 
11.82% of ash in dried plants of Equisetum hyemale, collected near New Haven, 
Conn. 
** “ Journal fiir praktische Chemie,” 1856, 69. 176. 
