LIFE HISTORIES 19 



reproduction to be observed in the Lycopo- 

 diums 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. 

 davatum). 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 pro- 

 thallus 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 im- 



