The life histories of the Club Mosses have certain points which make them of special interest. In the first place, the manner of reproduction to be observed in the Lycopodiums may be outlined. Sometimes the sporangia are borne on fertile leaves which exactly resemble the ordinary ones; a good instance of this is seen in the case of the Fir Club Moss (_Lycopodium selago_). On the other hand, the fertile leaves may be gathered together into cones such as are to be observed in the case of the Common Club Moss (_L. clavatum_). The sporangium is quite a large affair, easily discerned with the naked eye. The number of spores produced is enormous—so much so that these can be shaken out in a thick powder. In some of the Lycopodiums the spores have a remarkable habit of resting before the development of the prothallus. It is said that in the case of the Common Club Moss the prothalli do not appear until the end of the sixth year. Even then, several more years elapse before the prothallus is sufficiently mature to bear the organs of sex. In the case of _L. inundatum_ the length of time which elapses between the coming of the prothallus is nothing like so great. With all the Lycopodiums, however, the prothallus, which varies a good deal in the different species, bears both kinds of sexual organs. In most of the cases where the development of the spore is such a long business the prothallus is produced underground. With _L. inundatum_, however, the prothallus is green and leaf-like. The underground prothalli have no chlorophyll, and hence cannot live the life of an independent green plant. It has lately been demonstrated that these are always found in conjunction with a certain fungus; probably the benefits of the association are mutual. Making allowance for certain differences which are not of great importance to the general student, the fertilization of the egg cell in the prothallus of the Lycopodium is carried out on very similar lines to those which have been described in the case of the Fern.