—71— 



a species of this sub-genus, and it can only be done by a micro- 

 scopical examination of the epidermis and interior. The follow- 

 ing characterization has been adapted from Milde's "Mono- 

 graphia Equisetorum :" 



Equisetum L. 



Stomata forming a single broad line, composed of several 

 rows, or with two irregular lines, often scattered, set obliquely, 

 without regularly formed cells between them; the surface of the 

 stomata overlaid with a plate of silex, which is free at the edges, 

 and which shows a small vertical slit in the middle — correspond- 

 ing to the opening of the stomata. Plants with usually two 

 kinds of stems, spike blunt, rhizome without silicious dots, 

 species easily separated by prominent characteristics. 



A. EqUISETA HETEROPHYADICA A. Br. 



Stomata always forming two separate rows ; stems dimorphous ; 

 fertile at first branchless, pale, smooth, without stomata or bast, 

 evanescent, or developing branches, chlorophyl, stomata and 

 bast; sterile with dense verticils of branches, which are without 

 central cavity; inner cylinder (/. e., the parenchyma cells sur- 

 rounding the central cavity) composed of thickened cells. 



a. Equiseta anomopora Milde. 



Stomata wanting or forming two contiguous rows, made up 

 of 2-6 lines each, in the middle of the grooves, 

 (i.) E. arvense L. (2.) E. telmateia Ehrh. 



b. Equiseta stichopora Milde. 



Stomata widely separated, forming 1-2 lines, high up on the 

 ridges; fertile stems at first pale, branchless, smooth, without 

 stomata or bast, very soon developing branches, chlorophyl, 

 stomata and bast, and becoming rough. 



(3.) E. pi'aten se Ehrh. (4.) E. silvaticum^L,. 



B. Equiseta homophyadica A. Br. 



Stomata forming a single, very wide row in the grooves, con- 

 sisting of many lines ; branches wanting, scattered or in verticils, 

 with central cavity. 



a. Inner cylinder composed of thickened cells. (5.) E. 

 palusire L. 



b. Cells of inner cylinder not thickened. (6.) E. fluviatile 

 L. (7.) E. litorale Kuhlw. 



