54 BOTANICAL GAZETTE [yuty 
of chlorophyll work done by the less favored region, and its con 
sequent 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 sporogonium. I grant that this 
same reasoning would make the sporogonium of the Anthoceros 
forms a specially well adapted erect structure for the develop- 
ment of leaf tissue and hence leaves. The objection, however, 
is that the sporogonia of bryophytes are most persistently spore- 
bearing structures and nothing else, every tendency towards ) 
more complex organization having spore production and spore : 
dispersal in view; and that such specialized structures are not ~ 
apt to be productive of new lines of development. 
In considering, therefore, whether it is possible to disregard 
the bryophytes in our search for the origin of the leafy spore 
phyte, we are largely influenced by the fact that the bryophy te 
sporophyte, throughout its whole history, is dominated by 4 
tendency which does not appear in the pteridophyte sporophyt®. — 
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 appear 
ance of the bryophyte Sporogonium was dominated by the separa 
tion of spore formation from the other functions, chlorophyll 
work being retained by the gametophyte, along with gamete 
production. Attention has been focused so long upon me 
gametes and spores as the two dominant factors in differentia 
tion that it is hard to conceive of the possibility of the domina 
tion of another factor. It is entirely conceivable, however, that — 
another form of differentiation may have occurred, dominated _ 
by the needs of the chlorophyll work, and not by spore produc: 
tion. Certainly a great need for change, when aquatic conditio™ 
were exchanged for terrestrial, was in connection with the displ4y _ 
of chlorophyll tissue. It would seem as if the bryophytes had | 
laid emphasis upon spore production, and therefore never became | 
