60 PLANT-LIFE ON LAND [ch. iv 



evidence may be obtained of the correctness of this 

 view. 



Two common plants, which are widespread in 

 Great Britain, may be cited as illustrative examples, 

 viz. the Common 8hield-Fern {Nephrodium filix- 

 Qiias), and a common Club-Moss {Lijcopodiimi Selago). 

 In the former the plant consists of a simple shoot 

 bearing leaves which are all alike, but large and 

 freely branched. Though in young plants the leaves 

 bear no sporangia, in any well nourished plant that 

 is mature all the leaves are as a rule fertile. They 

 are in fact leaves that serve various purposes, for 

 when young they protect the tender apical bud, and 

 when expanded they serve the double purpose of 

 nutrition and of propagation by spores (Fig. 11). But 

 in Flowering plants these three functions are generally 

 carried out by three different types of leaves, the 

 scale-leaves protecting the bud, the foliage leaves 

 serving for nutrition, and the stamens and carpels 

 for propagation. In some Ferns these distinctions 

 are already suggested ; for instance, in the common 

 Hard Fern {Lomaria sjncaut) the sterile and fertile 

 leaves diifer in outline though fundamentally alike : 

 and in the Royal Fern {Osmnuda regalls) there are 

 some stunted leaves Avhich serve for protection only. 

 Such occasional distinctions seem to suggest that 

 our hypothesis of differentiation is really a correct 

 one. 



