196 THIRD GROUP. VASCULAR CRYPTOGAMS. 



female prothallium remains inclosed in the spore till the moment of fertilisation. 

 The sporophyte is a stem which is either simple or repeatedly branched, and has 

 roots ; the leaves are always perfectly simple, proportionally small but very numerous, 

 and traversed by one simple vascular bundle. The branching of the stem and roots 

 is monopodial or nearly so, but sometimes distinctly dichotomous. The sporangia 

 appear singly on the upper side of the base of a leaf, or in the axil or on the stem 

 above the axil of a leaf, or they are sunk in the tissue of the extremity of a short 

 branch, as in the Psilotaceae ; they are formed from groups of cells. The arche- 

 sporium is formed as in other Eusporangiatae. 



A. Lycopodiaceae. 



1. HOMOSPOROUS LYCOPODIACEAE. The spores are of one kind and produce 

 monoecious prothallia with an independent life. Stem and roots branch dichoto- 

 mously in planes which cross one another ; neither have an apical cell ; the leaves 

 have no ligule. Vascular bundle of the stem have several xylem-strands which are 

 separated by phloem and surrounded by it. 



To these belong the Lyccpodieae, with one genus, and the Phylloglosseae, also 

 composed of one small Australian genus, Phylloglossum, distinguished by its peculiar 

 formation of tubers ; the sporangia are, as in Lycopodium, on the base of bracts, on a 

 spike which is otherwise leafless. 



2. HETEROSPOROUS LYCOPODIACEAE ; fossil only ; Lepidodendron. 



B. Psilotaceae. Only one kind of spores known ; the germination not known ; 

 the sporangia are sunk in the extremities of short lateral branchlets with two leaves ; 

 there are notrue roots, but instead of them subterranean, creeping stems. Two 

 living genera, Psilotum and Tmesipteris. 



C. Ligulatae. Spores of two kinds, macrospores and microspores ; a female 

 prothallium of some size is produced inside the macrospore, and is only sufficiently 

 exposed through a fissure in the coat of the spore for the archegonia to be laid bare ; 

 the microspores also form a rudimentary prothallium which completely fills them, and 

 the mother-cells of the spermatozoids are produced from certain of its cells. The 

 habit of the sporophyte varies much in the two families ; the leaves have always a 

 ligule above their base, and below this is the sporangium, which matures either a 

 number of microspores or four or more macrospores. 



Families. 1. Selaginelleae. 



2. Isoeteae. 



(The groups which have been brought together under the name of Ligulatae 

 have scarcely anything in common but the presence of a ligule, and it would be better 

 perhaps to make separate divisions of them.) 



I. FILICINEAE. 



The character common to all the plants which are here united under the name 

 of the Filicineae, and which distinguishes them from the Equisetineae and Lycopo- 

 dineae, is the abundance and perfection displayed by their leaves ; these are always 

 large in proportion to the stem, and more highly developed in form and structure 

 than the leaves of the other divisions of the Vascular Cryptogams. In the Equise- 



