44 PLANT-LIFE ON LAND [CH. 



The special efRcienc}^ in the Bracken is no doubt 

 in large measure due to this habit. It has been seen 

 how readily it spreads b}" the growth and profuse 

 branching of the underground rhizome. This serves 

 as a means of perennation from season to season. 

 It also serves as a place of storage of reserve food 

 for future use. So successful are these means of 

 perpetuation and of spread that little dependence 

 need be made upon the formation of new plants 

 by germination of the spores and sexuality. There 

 is many an observant botanist who has never seen 

 a young seedling of Pterklium in the open, and we 

 can only conclude that in Nature the completion 

 of the life-story by sexuality is a comparatively 

 rare event. There can be no doubt, however, that 

 the power of raising a young plant through the 

 germination of every matured spore is present, for 

 under conditions of suitable culture the prothallus 

 is easily grown, and young plants follow. 



And thus the cycle of life of the Fern is completed. 

 It is plain that it consists of two distinct phases, or 

 generations as they are called, and the life-cycle is 

 punctuated by two periods when the organism consists 

 of only a single cell, viz. the spore which is produced 

 by the Fern-plant, and the zygote which is produced 

 by the prothallus. Between these landmarks intervene 

 two more extensive developments or generations, viz. 

 the prothallus and the Fern-plant. These succeed 



