ACROGENOrS PLANTS. 



560. Series II. — Cryptogamous or Flowerless Plants. 



Class III. — Acrogenoil^ Plants. 



561. Equisetacejs, the Horse-tail Triht. — Leafless plants. Stem 

 simple or branched, striated, hollow, clo- d and separable at the 

 joints, each of which is surrounded by a membraneous, toothed 

 sheath. Inflorescence a dense, cylindric, terminal spike or 

 strobile composed of peltate scales ; spore-cases {tJieccB 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 {thecce or sporangia^ arising from the veins 

 on the under surface of the fronds, or along the margin. TJiecce 

 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. Ophioglossese ; sporangia S23iked, distinct, exannulate. 



Genera. — 1. Polypode^ — Acrostichum, Polypodium, Adiantum, Pteris, Onoclea, 

 Asplenium, Scolopendrium, Aspidium. 2. Osmunde^ — Osmunda, Lygodium, Schi- 

 zaea. 3. Ophioglosse^ — Ophioglossum, Botrychium, Hypopeltis. 



Fig. 215, a, part of the leaf of Aspidium loncidtis ; b, magnified view of a sectioM 

 of A. exaltation. 



Fig. 216. 



Fig. 216, Alsophila (tree-fern). The tree-ferns are the most gigantic ol the 

 Acrogens ; their trunks are sometimes forty feet high ; in appearance they re 

 semble palms and some other endogenous plants, but in structure they differ ; 

 ^he stem ia formed by the union of leaves at their bases, ike vessels of which ex- 



