290 MORPHOLOGY OF AXGIOSPERMS 



been discussed by Coulter, 8 the substance of whose paper may 

 be stated in the following extracts : 



It has been common to regard the distinct sporophyte as having 

 been established once for all by the Bryophytes, and the sporophytes 

 of the higher groups to have been derived from those of the Bryo- 

 phytes. In searching for the origin of the leafy sporophyte, therefore, 

 attention has been focused upon the sporogonia of Bryophytes. . . . 

 The doctrine that any plant structure, however important, can have 

 but one phylogeny, is hardly tenable at present. ... In contrasting 

 the sporophytes of Bryophytes and Pteridophytes, they seem to have 

 nothing in common except that they are usually derived from the 

 oospore and represent an asexual generation. These facts are im- 

 portant, but so are the numerous other facts in which they differ 

 sharply. . . . 



It may be well to contrast the leafless and leafy sporophytes. In 

 the former case the structure is never independent of the gametophyte, 

 develops no lateral members, has nothing comparable to sporangia, 

 and its whole tendency is to render complex the spore-producing 

 region. In the latter case the sporophyte is dependent upon the game- 

 tophyte only in its embryonic stage, develops prominent lateral mem- 

 bers, has distinct simple sporangia, and its whole tendency is to render 

 complex the sterile or nutritive tissues. As one traces the evolution 

 of the Bryophyte sporogonia they give evidence of increasing com- 

 plexity and hence rigidity, and little promise of originating such a 

 diverse tendency as that shown by the sporophyte of Pteridophytes. 

 . . . The origin of leaves on the gametophore of mosses suggests that 

 leaves may develop in response to more favorable conditions for their 

 work, and such development may result in the great reduction of 

 chlorophyll work done by the less favored region, and its consequent 

 simplification. It is evident that with the exchange of an aquatic for 

 a terrestrial habit the thallose body would not be a favorable type for 

 chlorophyll work, and that the development of chlorophyll tissue upon 

 erect structures of various kinds might follow. Among Bryophytes 

 the erect structure laid hold of is the gametophore, and not the sporo- 

 gonium. . . . 



In considering whether it is possible to disregard the Bryophytes 

 in our search for the origin of the leafy sporophyte, we are largely 

 influenced by the fact that the Bryophyte sporophyte, throughout its 

 whole history, is dominated by a tendency which does not appear in 

 the Pteridophyte sporophyte. Before the establishment of alternate 

 generations the plant body may be said to have had three functions, 

 namely, chlorophyll work, and the production of gametes and spores. 

 The appearance of the Bryophyte sporogonium was dominated by the 

 separation of spore-formation from the other functions, chlorophyll 

 work being retained by the garnetophyte, along with gamete-produc- 



