SALVINIA FAMILY. 35 
2. AZOLLA Lam. Encycl. 1: 343. 1783. 
Minute moss-like reddish or green floating plants, with pinnately branched stems covered 
with minute imbricated 2-lobed leaves, and emitting rootlets beneath, Sporocarps of two 
kinds borne in the axils of the leaves, the smaller ovoid or acorn-shaped, containing a single 
macrospore at the base and a few corpuscles above it whose character is not fully known, 
the larger globose, producing many pedicelled sporanges, each containing several masses of 
microspores which are often beset with a series of anchor-like processes of unknown func- 
tion. [Greek, signifying killed by drought. ] 
About 5 species of wide geographic distribution. 
1. Azolla Caroliniana Willd. Carolina 
Azolla. (Fig. 76.) 
Aczolla Caroliniana Willd. Sp. Pl. 5: 541.  18to. 
Plants greenish or reddish, deltoid or triangu- 
lar-ovate in outline, pinnately branching, some- 
times covering large surfaces of water. Macro- 
spores minutely granulate, with three accessory 
corpuscles; masses of microspores armed with 
rigid septate processes; leaves with ovate lobes, 
their color varying somewhat with the amount 
of direct sunlight, the lower usually reddish, the 
upper green with a reddish border. 
Floating on still water, Ontario and western New 
York to British Columbia, south to Florida, Arizona 
and Mexico. Also in South America. Naturalized 
in lakes on Staten Island, N. Y. 
Family 8. EQUISETACEAE Michx. Fl. Bor. Am. 2: 281. 1803. 
HORSETAIL FAMILY. 
Rush-like perennial plants, with mostly hollow jointed simple or often much- 
branched grooved stems, provided with a double series of cavities and usually 
with a large central one, the branches verticillate, the nodes provided with dia- 
phragms. Rootstocks subterranean. Leaves reduced to sheaths at the joints, 
the sheaths toothed. Sporanges 1-celled, clustered underneath the scales of ter- 
minal cone-like spikes. Spores all of the same size and shape, furnished with 2 
narrow strap-like appendages attached at the middle, coiling around the spore 
when moist and spreading, when dry and mature, in the form of a cross (elaters). 
Epidermis impregnated with silica, rough. Prothallium on the surface of the 
ground, green, usually dioecious. 
The family consists of the following genus : 
Es EQUISETUM WaSpebletoon. | 47/53; 
Characters of the family. [Name ancient,signifying horse-tail, in allusion to the copious 
branching of several species. | 
About 25 species, of very wide geographic distribution. 
Stems annual ; stomata scattered. 
Stems of two kinds, the fertile appearing in early spring before the sterile. 
Fertile stems simple, soon withering; sheaths of branches of sterile stems 4-toothed. 
1. £. arvense. 
Fertile stems branched when old, only the apex withering. 
Branches of the stem simple, their sheaths 3-toothed. 2. BE. pratense. 
Branches compound. 3. EZ. sylvaticum, 
Stems all alike; spores mature in summer; branches simple or none. 
Sheaths rather loose ; branches usually long ; stems bushy below, attenuate upwards. 
Central cavity very small ; spike long. 4. BE. palustre. 
Central cavity about one-half the diameter of stem; spike short. 5. E. littorale. 
Sheaths appressed ; branches usually short. 6. E. fluviatile, 
Stems perennial, evergreen ; spikes tipped with a rigid point ; stomata in regular rows. 
Stems tall, usually many-grooved. 
Stems rough and tuberculate, prominently ridged. 
Ridges with 1 line of tubercles; ridges of sheath tricarinate; stem stout. 
7. E. robustum. 
Ridges of the stem with 2 indistinct lines of tubercles; ridges of sheath obscurely 
4-carinate; stem slender. 8. E£. hyemale. 
Stems not tuberculate; sheaths enlarged upward. 9. E. laevigatum, 
Stems low, slender, tufted, usually 5-10-grooved. 
Central cavity small ; sheaths 5-10-toothed. 10, &. vartegatum, 
Central cavity none ; sheaths 3-toothed. 11. £. sctrpotdes, 
