PTERIDOPHYTA— HORSETAIL 323 



sporangia 1 -celled clustered underneath the shield-shaped scale of the cone; 

 spores all alike, two thread-like elastic filaments (elaters) are attached to the 

 base of the spore which roll around it when moist and spreading when ripe; 

 prothallus green formed upon damp ground, usually dioecious. One order, 

 Bguisetaceae, and one genus, consisting of 40 species. Fossil horsetails numer- 

 ous. 



EQUISETACEAE 



Equisetum. L. Horsetail 



Perennial jointed plants with creeping root-stocks, dull and blackish in color, 

 often bearing tubers, roots in whorls from the nodes, stems usually erect, simple 

 or branched, jointed cylindrical, the surface striated, the stomata occur in grooves 

 either in rows or in bands, the nodes bearing a whorl of reduced leaves joined 

 by their edges into cylindrical sheaths, the tips consist of presistent or deciduous 

 teeth; branches when present in the form of whorls from the nodes; fruit 

 consisting of a terminal cone containing the sporangia in which occur the green- 

 ish spores ; each spore provided with four hygroscopic bands, the elaters ; 

 spores produce two kind of prothalli, one male the other female; the male con- 

 taining the antheridia, the female the archegonia. A small genus commonly 

 called rushes or horsetails. Some ten species in eastern North America. 



Equisetum arvense. I,. Common Horsetail 



Perennial with annual stems, stomata scattered; fertile stems unbranched, 

 destitute of chlorophyll, 4-10 inches high, soon perishing; sheaths distant, 

 8-12 toothed; the sterile slender 1-2 feet high, 10-14 furrowed producing simple 

 or sparingly branched, 4-angular teeth, herbaceous, triangular lanceolate. 



Distribution. Abundant in sandy fields along roadsides and railroads, es- 

 pecially northward from Newfoundland to Virginia, California and Alaska. 

 Also occurs in Europe and Asia. 



Equisetum hyemale. L. Scouring Rush 



Stems all alike, slender, rather stiff, evergreen, from lJ^-4 feet high, 

 8-34 grooved. Stem rarely producing branches which are usually short and 

 sometimes fertile; stomata arranged in rows, rough ridges with 2 indistinct 

 lines of tubercles, the central cavity large, sheath rather long, cylindrical, 

 marked with a black girdle, their ridge obscurely carinate; spikes persistent. 



Equisetum hyemale. L. var. robustum, (A. Br.) A. A. Eaton 



Stem perennial, tall and stout, 8-10 feet high, sometimes an inch thick, 

 occasionally branched; 30-48-grooved, the ridges roughened with lines of trans- 

 versely-oblong tubercles; sheaths rather short with a thick girdle at the base 

 and a black limb; ridges of sheaths carinate. 



Distribution. In wet places, from Ohio, Iowa, to Louisiana, Mexico, Cal- 

 ifornia, and British Columbia, also in Asia. 



Poisonous properties. The rushes have long been recognized in Europe 

 as being injurious to horses, and there are records of their poisonous proper- 

 ties in American Agricultural Literature. 



A writer in the American Agriculturist, many years ago, described accu- 

 rately a disease which might be called equisetosis, and which was produced by 

 poisoning from these rushes. 



