When we come to consider the past history of the Club Mosses the record is of a different nature to that of the Ferns. Nowadays the Club Mosses are not of great importance in the world, even though, as will be shown later, the number of species is considerable. But when we travel back to Palæozoic times, particularly in the coal period, it is evident that these plants were represented by a number of very large and dominant families. Some of these early Club Mosses certainly came very near to rivalling the Flowering Plants. Probably the tendency of the world to become drier has had something to do with the decline, seeing that in all cases the fertilization is carried out under water. We may gather some idea of the importance of the Club Mosses in Palæozoic times from the fact that in every part of the world where coal deposits have been examined great numbers of the fossil remains of these plants are always discovered. Many of these grew into large trees which were a hundred or more feet in height, sending out great branching shoots above and an enormous root system below. From a botanical point of view there is no doubt that some of the Club Mosses, particularly those belonging to the family _Selaginellaceæ_, have approached very nearly to the Flowering Plants. At the present time the existing species, the Selaginellas, bring us up to the very threshold of the dominant group. The lowest division of the Flowering Plants is the _Gymnospermæ_ (which includes the Conifers), and it is interesting to note the points of similarity between a typical Gymnosperm and a Selaginella. To start away with, the Selaginella bears two kinds of spores, each of which in its development has a definite sex character. The smaller ones (microspores) are in their manner of production analogous to the pollen-grains of the Flowering Plant. The prothallus and the male organ (antheridium) are comparable to the special cell-group in the pollen-grain, whilst the spermatozoids approximate to the generative cells. In the larger spores (megaspores) these represent the embryo sac, and the sporangium in which they are produced closely approximates to the part containing the embryo sac in the Flowering Plant. The prothallus which arises from the megaspore in the Selaginella closely resembles the endosperm—a special tissue formed to feed the embryo in the case of flowering plants. The female organ (archegonium) and the cell which it produces are practically identical in both cases. Fossil remains have shown that some of the plants like Selaginella which flourished in Palæozoic times seemed to have come very near to the production of seed. Thus one species which has been described shows a megaspore which was permanently within the sporangium, and which in its general development greatly resembled a fruit. It is, of course, impossible to give more than a very brief outline of some of the chief points in this highly important comparison between the Gymnosperm and the Selaginella.