6 ISOETACEAE 



1. AZOLLA Lam. 



Minute moss-like water plants with pinnately branching stems and 

 imbricated leaves. Sporocarps of two kinds, in pairs in the axils. 



1. A. Caroliniana Willd. Plants reddish or greenish, 6'^ or less 

 high : leaves minute, with ovate lobes at the base. — In ponds at Ather- 

 ton, Lake City and Sibley. Common at times. July-Ootober. 



F.AMiLY 5. EQUISETACEAE Michx. 

 Eush-like often branching herbs, with hollow, jointed, striate stems, 

 bearing sheaths at the joints. Sporanges 1-celled, borne underneath the 

 shield-shaped scales of the terminal cone-like spike. Spores all similar, 

 numerous, each provided with four ligule-like appendages. 



1. EQUISETUM L. 

 Characters of the family. 



Stems 11° or less high. 



Sheaths of sterile stems 4-toothed. 1. E. arvense. 



Sheaths of sterile stems 5-10-toothed. 2. E. xuiriegatum. 

 Stems 2°-l()° high. 



Stems slender. 3. K. hycmole. 



Stems robust. 4. E. mhustum. 



1. E. arvense L. Horse-tail. Fertile stems without chlorophyll, 

 preceding the sterile, unbranched : sheaths about five, 7^^-8'^ long, white, 

 bearing twelve brown acuminate teeth : fructification abont 1' long, 

 cylindric : sterile stems green, slender, branched : branches four-angular. 

 — Common on wet banks, the fertile stems appearing in April. 



2. E. variegatum Schleich. Slender Scouring-rusii. Stems tufted, 

 all with chlorophyll, slender, 5-10-grooved : sheaths partly black. — 

 Muddy sand-bars along the Missouri River. Common at times. Never 

 collected in fruit here. 



3. E. hyemale L. Com.mon SconKiNO-RUSir. Stems unbranched, the 

 numerous ridges each bearing two lines of tubercles : sheaths .short, with 

 a black ring at base and a black base to the Ciiducoiis teeth : fructifica- 

 tion less than 6''' long. — Of rare occurrence on wet banks along the Mis- 

 souri Kiver at Courtney. 



4. E. robustum K. Br. Stout Scoueing-rush. Like the preceding, 

 but very robust, the ridges of the stem each bearing one line of tubercles. 

 — Very common in bottoms, especially along the Missouri Kiver. 



F.XMiLY G. ISOETACEAE Underw. 

 Rush-like herl)S with numerous linear awl shaped leaves from a subter- 

 rfineaii rather small trunk. Sporanges sessile in the axila of the leaves, 

 rather large, orbicular or ovoid and plano-convex, partly covered by a 

 fold from the inner side of the leaf-blade (the velum), the outer beariDg 

 niaorospores, the inner microspores. 



