SALVINIA FAMILY. 



35 



2. AZOLLA Lam. Encycl. i: 343. 1783. 



Minute moss-like reddish or green floating plants, witVpinnately branched stems coveted 

 with minute imbricated 2-lobed leaves, and emitting rootlets beneath. Sporocarp* of two 

 kinds borne in the axils of the leaves, the smaller ovoid or acorn-shaped, containing MOB! 

 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 fnnc- 

 tion. [Greek, signifying killed by drought.] 



About 5 species of wide geographic distribution. 



I. Azolla Caroliniana Willd. Carolina 

 Azolla. (Fig. 76.) 



Azolla Caroliniana Willd. Sp. PI. 5 : 541. 1810. 



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. 



% ^J 



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 i -celled, clustered underneath the scales of ter- 

 minal cone-like spikes. Spores all of the same size and shajx.-, 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 

 Epidermis impregnated with silica, rough. Prothallium on the surface of the 

 ground, green, usually dioecious. 



The family consists of the following genus : 



i. EQUISETUM L. Sp. PI. 1061. 1753. 

 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 tin- -t< 



Fertile stems simple, soon withering; sheaths of branches of sterile stems. 





Fertile stems branched when old, only the apex withering. 

 Branches of the stem simple, their sheaths 3-toothe<l. 

 Branches compound. 

 Stems all alike; spores mature in summer; branches simple or none. 





IUB an aiiiwc: , ojjtjico IIKILUI i in oi*iu***v-*j *** .-j-- 



Sheaths rather loose ; branches usually long ; stems bushy below, attenuate up 

 Central cavity very small ; spik* long. 

 Central cavity about one-half the diameter of stem; spike short. 



Central cavity - 



Sheaths appressed ; branches usually short. 

 Stems perennial, evergreen ; spikes tipped with a rigid point ; stomata in 

 Stems tall, usually many-grooved. 



Stems rough and tuberculate, prominently ridge ' 



Ridges with i line of tuberctes; ridges of sheath tncanr rotmttmm. 



jjj 1 



Ridges of the stem with 2 indistinct lines of tubercles; rid*** 



4-carinate ; stem slender. 

 Stems not tuberculate; sheaths enlarged upward. 

 Stems low, slender, tufted, usually 5-io-grooved. 

 Central cavity small ; sheaths 5-io-toothed. 

 Central cavity none ; sheaths 3-toothed. 





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