294 
A.CROGENOUS PLANTS. 
560 Series II. — Cryptogamous or Flowerless Plants. 
Class III. — Acrogenous Plants. 
661. Equisetace^, the Horse-tail Tribe. — Leafless plants. Stem 
simple or branched, striated, hollow, closed and separable at the 
joints, each of which is surrounded l3y a membraneous, toothed 
sheath. Inflorescence a dense, cylindric, terminal spike or 
strobile composed of peltate scales ; spore-cases {thecm or sporan- 
gia) attached to the lower surface of the scales. Spores numer- 
ous, oval, surrounded by a pair of elastic, clavate elaters. 
a. Properties: plants of this order abound in silex, and are useful in polishing 
furniture. 
Genus. — Equisetum. 
562. FiLicES, Ferns. — Stem a creeping rhizome, or an erect, 
arborescent trunk. Leaves {fronds) usually circinate in verna- 
tion. Spore-cases {tJieccB or spwangia) arising from the veins 
on the under surface of the fronds, or along the margin. Thecm 
either stalked, with the pedicel passing round them in the form 
of an elastic ring, or sessile and destitute of a ring. The three 
principal sub-orders are: 1. Polypodiese; thecse on the back of 
the frond annulate, bursting irregularly and transversely; 
spores roundish or oblong. 2. Osmundese ; sporangia variously 
collected, destitute of a proper ring, opening lengthwise. 
3. OphioglosseaB ; sporangia spiked, distinct, exannulate. 
Genera. — 1. Polypode^ — Acrostichum, Polypodium, Adiantum, Pteria, Onoclea, 
Asplenium, Scolopendrium, Aspidium. 2. Osmunde^ — Osmunda, Lygodium, Schi- 
zado,. 8. Ophioglosse^ — Ophioglossum, Botrychium, Hypopeltis. 
Fig 215, a, part of the leaf of Aspidium lonchitis ; b, magnified view of a section 
of A. exaltatmti. 
Fig. 215. Fig. 216. 
Fig. 216, Alsophila (tree-fern). The tree-ferns are the most gigantic ot ttoe 
Acrogens ; their trunks are sometimes forty feet high ; in appearance tliey re 
Bemble palms and some other endogenous plants, but in structure they differ ; 
^je stem is formed by the union of leaves at their bases, the vessels of wliich ex- 
