a See ee ee ee a a Se 
1899 ] ORIGIN OF THE LEAFY SPOROPHYTE 51 
y 
Riccia, while further encroachment upon the sporogenous tissue, 
with more or less differentiation of the sterile tissue, would 
account for the series of sporogonia displayed by bryophytes. 
Whether the origin of this structure is to be regarded as homol- 
ogous or antithetic is not pertinent to the present discussion, 
but it seems reasonable to see in it an entirely new structure 
developed by the oospore, and in no way homogenetic or even 
homologous with the gametophyte. It has been noted that the 
argument drawn from apogamy in favor of homologous origin 
finds little or no application among bryophytes, for the origin of 
the sporogonium seems to be as fixed as the origin of any plant 
structure can be. 
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 bryophytes. In searching for the origin of the 
leafy sporophyte, therefore, attention has been focused upon 
the sporogonia of bryophytes, and the Anthoceros forms have 
been selected as most nearly representing the ancestral condition. 
The doctrine that any plant structure, however important, 
can have but one phylogeny, is hardly tenable at present. That 
heterospory has appeared independently in several lines has 
become evident ; and that it has resulted more than once in seed 
formation is hardly less evident. The conditions which 
determined these modifications must have been common enough 
to have established similar results more than once. Why the 
Sporophyte may not fall in the same category is not clear. 
Professor Bower’s statement that the polyphyletic origin of a 
ihe a is an easy escape from difficulties suggests caution, 
Ase - not close the door to the fact that nature may have 
€ same easy way out of difficulties. 
id the sporophytes of bryophytes and pterido- 
ae co eg abide to have nothing in common except that - 
be he from ie oospore and represent an asexua 
oe mae hese facts are important, but so are the numerous 
in which they differ sharply. There are also asexual 
