The next order of the Vascular Cryptogams is of comparatively small importance as far as the present study is concerned. It is known as the _Rhizocarpeæ_ (Pepperworts). The order is divided into two families as follows:— 1. _Salviniaceæ._—The only two genera are Salvinia and Azolla; the latter has been already mentioned. 2. _Marsiliaceæ._—The British example is the Pillwort (_Pilularia globulifera_). The Club Mosses have been divided into six families. Two of these—the _Lepidodendraceæ_ and the _Sigillariaceæ_—are only represented by fossils; and one, _Psilotaceæ_, has no British representatives. The remaining families all include one or more species which are indigenous to our islands. 1. _Lycopodiaceæ._—These are the Club Mosses proper. Several species of the genus _Lycopodium_ are British. The Common Club Moss (_Lycopodium clavatum_) is often abundant on high moors. 2. _Selaginellaceæ._—A large family containing three or four hundred species, only one of which, however, is British; this is _Selaginella spinosa_. 3. _Isoëtaceæ._—A family of aquatic Club Mosses. The British species is _Isoëtes lacustris_, a plant which is sometimes common in the northern lakes. With this brief survey of the Vascular Cryptogams one may naturally pass to a somewhat more detailed consideration of the life histories of these interesting plants than it has been possible to give in an opening chapter. CHAPTER II LIFE HISTORIES Even the most general survey of the Vascular Cryptogams would not be complete without an attempt to indicate the means of reproduction to be observed in these plants. The subject is one which might well be treated at great length, for there is scarcely any species which does not present some interesting point that calls for comment. Within the limits of the present inquiry it will not be possible to give more than an outline of the reproductive schemes to be observed in a few typical species. These life histories must not be taken as necessarily applying to all the related plants. None the less, by a careful study of the species described we may receive a fair conception of the habits of the class to which it belongs. Incidentally it may be mentioned that even a low-power microscope will be an enormous help in studying the life histories of the Vascular Cryptogams; but if this is not possible, a pocket-lens will help to a better understanding of many of the points described.