66 BOTANY. 
burst open. This species is common in the United States. Ceterach 
officinarum (fig. 49°); C leptophylla (fig. 48.) ; 
Orver 9. Eauiseracex, Horse tails. Stem striated, hollow, usually 
branched, containing much silica in its composition, articulated, the joints 
being separate, and surrounded by a membranous toothed sheath. There 
are no true leaves, green-colored branches having a straight vernation, 
occupying their place. The cuticle exhibits a longitudinal series of 
stomata. A spiral structure is observed in some of the vessels.. Reproduc- 
tive organs collected into cones; spore-cases (thecze or sporangia) attached to 
the lower surface of peltate polygonal scales, and opening by an internal 
longitudinal fissure ; spores in the form of rounded cells, surrounded by two 
elastic club-shaped, hygrometric filaments, or elaters. Plants, with simple or 
branched stems, the branches being jointed and placed in whorls at the 
articulations of the stem, each whorl consisting of as many branches as there 
are teeth in the sheath. Found in ditches, lakes, and rivers, in various parts 
of the world. 
From the quantity of silicic acid contamed in them, some of the species 
of Hquisetum are used in polishing woods and in scourmg utensils. The 
spiral filaments which surround their spores are interesting objects under 
the microscope, exhibiting marked movements according to the moisture 
or dryness of the atmosphere around them. The stomata are arranged in 
lines on the cuticle. In Hquisetum hyemale, often called Dutch rushes, 
the silicious stomatic apparatus is well seen after the action of nitric acid on 
the stem. There are regular rows of tubercles of a silicious nature, in each 
of which is a transverse fissure, and at the bottom of the fissure a stoma is 
placed, with its opening at right angles to that of the tubercle. Hach 
portion of the stoma has a pectinated (comb-like) appearance. The distinctions 
between the species of Equisetum are founded on the nature of the fertile 
and barren stems, the number of striz or furrows, and the number of teeth at 
the articulations. 
There is but a single genus Equisetum, represented in North America by 
numerous species. One of these is Equisetum hyemale; another is HE. 
hmosum (pl. 54, fig. 59). 
Section B. PHanerRoGAamMous PLANTs. 
Class 2. Monocotyledones, Juss. Endogene, D.C. Amphibrya, Endl. 
7) So ,, 
In this great class the plants have a cellular and vascular system, the 
latter consisting partly of elastic spiral vessels. The woody stem is usually 
more or less cylindrical, simple, and unbranched. There is no true 
separable bark, no concentric zones, and no true pith. The wood is 
endogenous, 7. e. increases by additions which first tend towards the centre, 
and then curve outwards in an interlacing manner towards the circum- 
ference, where much hard ligneous matter is deposited, so as to make the 
exterior the hardest part. The development of the stem usually takes 
66 
