320 
IOWA ACADEMY OF SCIENCE Voe. XXIX, 1922 
Wet ground, rare. 
Railroad bank one mile west of Turner. 
N. Europe and n. e. N. America 
Note: Like other species of Equisetum, this species is very rich in 
silica, that is, the hard material of sand and glass. The outer surface is 
covered with almost pure silica. Our grandmothers used a bundle of the 
dried stalks to scour pots and pans ; hence the common name. The local 
form is var. robustum. 
Series 2. Pteropsida : Herbs, shrubs or trees, with primarily 
large lvs, whose attachment to the stem greatly modifies the 
structure of the latter at the nodes. Sporecases primarily numer- 
ous, borne on the underside of a leaf. The lower forms are 
reproduced by spores; the higher ones by seeds, resulting from 
flowers with pollen and ovules. 
Class 1. AspErmaE Seedless Pteropsidans. Ferns. 
Propagation by means of minute spores, borne in small cases 
(sporangia) on the backs or surfaces of ordinary or modified lvs. 
Stems always (in our species) under ground, only the lvs. 
coming up. Without cambium (except in Botrychium) ; vascular 
bundles variously disposed, concentric in structure. Veining of 
lvs. forked, occasionally the forks uniting into a network. 
Key to the Genera of Aspermae 
1. 
Sporangia on a naked stalk rising from the leaf 
Botrychium 
1. 
Sporangia on much contracted lvs. or If Its., without any green part 2 
1. 
Sporangia on the backs of ordinary lvs. 
3 
2. 
Sporangia exposed all over the modified If Its. 
Osmunda 
2. 
Sporangia enclosed in podlike rolled-up If Its. 
Onoclea 
3. 
Lvs. simple 
Camptosorus 
3. 
Lvs. compound 
4 
4. 
Lvs. once pinnately divided 
5 
4. 
Lvs. twice or more divided 
6 
5. 
Lflts. contracted to a short stalk 
Polystichum 
5. 
Lf Its. broadly attached to midrib 
Poly podium 
6. 
Sporangia covered by turned-back margin 
of leaf 
7 
6. 
Sporangia not covered by margin of leaf 
9 
7. 
Sporangia in separate patches 
Adiantum 
7. 
Sporangia all around If It. 
8 
8. 
Plant 5 cm. to 2 dm. tall 
Pellaea 
8. 
Plant 3-10dm. tall 
Pteridium 
9. 
Spore dots elongate, straight or curved 
Asplenium 
9. 
Spore dots circular 
10 
10. 
Lvs. 3-8 times longer than wide 
H 
10. 
Lvs. triangular, as wide as long 
Phegopteris 
11. 
Lvs. 4-8 cm. wide; stalks 2-3 mm. thick 
12 
11. 
Lvs. 8-15 cm. wide; stalks scaly, 3-5 mm. 
thick 
Aspidium 
12. 
Lvs. hairless 
Cystopteris 
12. 
Lvs. finely downy 
Woodsia 
