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-October. 



FAMILY 5. EQUISETACEAE Michx. 



Rush-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 1J or less high. 



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



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

 Stems 2-10 high. 



Stems slender. 3. E. hyemale. 



Stems robust. 4. E. robustum. 



1. E. arvense L. HOKSE-TAIL. Fertile stems without chlorophyll, 

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

 bearing twelve brown acuminate teeth : fructification about \' 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-RUSH. 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. COMMON SCOURING-RUSH. 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 caducous teeth : fructifica- 

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

 souri River at Courtney. 



4. E. robustum R. Br. STOUT SCOURING-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 River. 



FAMILY 6. ISOETACEAE Underw. 



Rush-like herbs with numerous linear awl-shaped leaves from a subter- 

 ranean rather small trunk. Sporanges sessile in the axils 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 bearing 

 macrospores, the inner microspores. 



