132 OUR NATIVE FERNS AND THEIR ALLIES. 



the fertile segment recurved its whole length, the shorter sterile 

 segment reclined upon it. (Fig. 35.) New England to Lake 

 Superior and Colorado to Alaska. 



2. OSMUNDOPTERIS Milde. Bud pilose, 

 enclosed in a smooth upright cavity at one side 

 of the lower part of the stalk. 

 7. B. Virginianum Swz. (RATTLESNAKE- 

 FERN.) Plant from a few inches to two feet 

 high ; sterile segment sessile above the middle 

 of the stalk, broadly triangular, thinly herba- 

 ceous, ternate; the short-stalked primary divi- 

 sions once to twice pinnate, then once or twice 

 pinnatifid ; lobes oblong, cut-toothed toward 

 the apex; fertile segment long-stalked, bi tri- 

 pinnate. Bud pilose, enclosed in a smooth 

 FIG. 35. Vernation upright cavity at one side of the lower part of 

 Angf ' (AftS-'Dave?- the stalk ; ferlile segment recurved its whole 

 port.) length, the longer sterile segment reclined upon 



it. Reduced forms are B. gracile Pursh. {Botrypus Virginicus 

 Michx., Osmunda Virginica L.) New Brunswick to Florida, 

 and westward to Arizona and the Pacific Coast. 



ORDER V. EQUISETACE^E DC. 



Plant body rush-like, often branched, with jointed, usually 

 hollow stems rising from subterranean rootstocks, the sterile 

 leaves reduced to sheaths at the joints, the fertile forming a 

 short spike terminating the stem. Prothallium above ground, 

 green, variously lobed, usually dioecious. Represented at pres- 

 ent by only one genus. 



I. EQUISETUM L. HORSE-TAIL. SCOURING-RUSH. 



Perennial plants with extensively creeping rootstocks. Stems 

 simple or branched, furrowed lengthwise, hollow, and pro- 

 vided with an outer circle of smaller cavities opposite the fur- 

 rows as well as a second and smaller series opposite the ridges. 

 Sporangia adhering to the under side of the shield-shaped 

 scales of the spike, one-celled, opening down the inner side. 

 Spores furnished with two slender filaments attached by the 



