64 BOTANY. 



during the wet season. Lycopodiiim clavatum, or common club-moss {pi. 54, 

 fig. 58.) 



Order T. Marsileace^, or Rhtzocarpe^, the Pepperwort Family. 

 Stem wanting, or a rhizome. Leaves often stalked, with the lamina 

 divided into three or more wedge-shaped pieces. Sometimes the lamina is 

 abortive ; vernation circinate. Reproductive organs near the root, or along 

 the petiole, inclosed in an involucre ; these organs are of two kinds : 1. 

 Stalked or sessile clustered membranous sacs, containing minute granules, 

 Avhich some consider as pollen : hence the bodies are called anthers. 2. 

 Membranous sacs, containing cells which divide into four, one only of which is 

 developed as a germinating \>oAy ; the sacs have been called ovule-sacs, and 

 the single developed cell is considered by some as an ovule which is impreg- 

 nated by the so-called pollen. The thecae are the bodies from which 

 germination proceeds, creeping or floating plants, found in ditches and pools 

 in various parts of the Avorld, more especially in temperate climates. They 

 are not put to any important use. There are four genera, and upwards 

 of twenty species. Examples : Marsilea, Pilularia, Salvinia. Marsilea 

 quadrifolia {pi. 54, fig. 47) ; Pilularia globulifera {fig. 45) ; Salvinia natans 

 (p/.54,^o..46). 



Order 8. Filices, or Ferns. Stem a rhizome, which creeps along or 

 under the surface of the ground, emitting descending roots and ascending 

 fronds (leaves), or which rises into the air so as to form an acrogenous 

 trunk. This trunk (stipe) is of nearly uniform diameter, is hollow in the 

 interior, marked on the hard outer rind by the scars (cicatrices) of the 

 leaves, and contains vascular bundles of woody, dotted, and scalariform 

 vessels, which are inclosed in hard plates, and are arranged in an irregular 

 manner. Sometimes the trunk is dichotomous. The outer fibrous 

 covering is formed by the bases of the leaves, and is thicker at the lower 

 than at the upper part of the stem. The leaves (fronds) have a circinate 

 (gyrate) vernation ; their veins are generally of equal thickness, and either 

 simple or dividing in a forked manner, or somewhat reticulated, and 

 occasionally stomata occur. Eeproductive organs consisting of spore- 

 cases (thecae, sporangia), which arise from the veins on the under surface 

 of the fronds, or from their margin. Spore-cases either stalked, with the 

 pedicel passing round them in the form of an elastic ring, or sessile and 

 destitute of a ring. The thecfe sometimes arise from the surface of the 

 frond, while at other times they spring from below, having a cuticular 

 coverino; in the form of an indusium or involucre. The clusters of thecas 

 are called sori. The margin of the frond sometimes is folded so as to cover 

 the thecfs, and at times the whole frond is converted into clusters of 

 thecffi. Certain cellular papillae, on the margin or upper surface of the 

 fronds, haVe been considered by some as antheridia, each of the cells 

 containing a spiral fibre. Link and others state, that among the young 

 thecce (pistiUidia) filamentous bodies occur, which are equivalent to 

 stamens. Ferns are elegant, leafy plants, occurring chiefly in moist 

 insular climates, and abounding in the tropical islands. In mild and warm 

 climates they occur in the form of large tree-ferns, fifty to sixty feet 

 64 



