Proceedings of the Ohio State Academy of Science. 291 



3. Fertile stems soon withering, silex of the sterile stems in dots; 

 branches of the sterile stems simple or compound E. arvense. 



3. Fertile stems branched and becoming green when old, only the 



apex withering. 4. 



4. Branches of the sterile and fertile stems simple; silex of broad 



spinules on the ridges E. pratense. 



4. Branches compound; silex of the fertile stems in 2 rows of promi- 



nent spinules E. syhaticum. 



5. Stems low and slender, tufted, usually 5-10 grooved, central cavity 



one-third the diameter of the stem; sheaths 5-10-toothed. . 



E. variegatum. 



5. Stems tall and rigid, rough and tuberculate, usually many-grooved; 



central cavity large, sheaths appressed. 6. 



6. Ridges of the stem with 2 indistinct lines of tubercles; ridges of 



the sheath obscurely 4-carinate ; stems less robust than in the 



following E. hyemale. 



6. Ridges with .1 line of tubercles; ridges of the sheath tricarinate; 

 stem very stout E. 7'obustum. 



1. Eqiiisetuin arvense L. Field Horsetail. 



Stems annual, 6 inches to 2 feet high, vv^ith scattered stomata, 

 the fertile appearing in early spring before the sterile. Fertile 

 stems not branched, soon withering; sterile stems green, much 

 branched, rather slender. Stomata of the branches in two rows 

 in the furrows. Quite a variable species. In moist soil and 

 on hillsides and railroad embankments. General and abundant 

 in the state. 



2. Equisetnin pratense Ehrh. Thicket Florsetail 



Stems annual, 6-i8 inches high, with scattered stomata, the 

 fertile appearing in spring before the sterile. Fertile stems 

 branched when old, only the apex withering. In sandy soil. 

 Apparently general in Ohio. 



3. Eqnisetum sylvdticuni L. Wood Horsetail. 



Stems annual with scattered stomata, 1-2 feet high; the 

 fertile appearing in early spring before the sterile, developing 

 whorls of compound branches when old. Silex of the fertile 

 stems in two rows of prominent spinules. In moist, sandy 

 woods. Auglaize and Cuyahoga counties. 



