134 HEREDITY AND EVOLUTION IN PLANTS 



a foliage leaf or a sporophyll, and considers that it probably 

 as we now know it, "represents its highest capacity for 

 evolution." 



On the hypothesis of progressive sterilization and ena- 

 tion (strobiloid theory), one would expect more primitive 

 sporophytes to possess relatively small leaves, that is, to 

 be microphyllous, and those with relatively large leaves 

 (megaphyllous) to be of later evolutionary development. 

 But there is no fossil evidence that the microphyllous fern 

 allies (club-mosses, horsetails, sphenophylls) are older 

 groups than the megaphyllous true ferns. The suggestion 

 is at hand, according to Tansley, that smaller leaved forms 

 have been derived from the larger leaved group by reduc- 

 tion. The facts of embryology and gametophyte anatomy 

 of the Lycopods are also interpreted by Sykes 1 as, on the 

 whole, supporting the hypothesis that the simpler Lyco- 

 pods are reduced forms and not primitive, the entire genus 

 Lycopodium being regarded as formed by reduction from 

 some of the larger fossil cone-bearing fern-allies, such, for 

 example, as Lepidodendron or one of its near relatives. 

 Miss Sykes has further suggested that the fossil genus 

 Spencerites may represent the connecting link, between the 

 two groups. 



It is not possible nor essential, in a book of this nature 

 and scope, to give a detailed discussion of the evidence and 

 the literature bearing upon this and similar questions. 

 It is only intended here to call attention to the fact that 

 different inferences as to the origin of the leafy sporo- 

 phyte and the broad course of plant evolution may be 



1 Sykes, M. G. Notes on the morphology of the sporangium-bearing 

 organs of the Lycopodiacese. New Phylologist. 7:41-60. Feb. and 

 Mch., 1908. 



