* 
1899] ORIGIN OF THE LEAFY SPOROPHYTE 49 
been derived from alge forms, and how alternation in ferns 
might have arisen if it did not come antithetically. 
The paper of Dr. Klebs deals with the subject of alternation 
of generations in thallophytes, and therefore concerns this present 
discussion but indirectly. His experiments among the lower 
forms, as is well known, have proved that there is no such rigidity 
in life histories as was once supposed. As a consequence, he 
does not consider that there is any such thing even as a regular 
homologous alternation of sexual and asexual phases. He thinks 
that experiments may prove that the so-called ‘fruit bodies” 
of such forms as Edogonium and Coleochete may turn out to be 
the result of certain conditions, rather than an inevitable part of 
the life history. He seems to consider that the origin of pteri- 
dophytes probably has nothing to do with that of bryophytes, 
and that there is at present no clue whatsoever as to the origin 
of the former. Such a peculiar structure in common as the 
archegonium he suggests may be a purely parallel development, 
without necessarily indicating any phylogenetic connection. 
It will be seen from the above papers that, while the origin 
of the sporogonium of bryophytes seems to be suggested, the 
origin of the leafy sporophyte is too obscure to justify any 
definite claim, According to Bower it is most probable that it is 
developed from such a sporogonium structure as is displayed by 
the bryophytes today; according to Lang and Klebs there is a 
Possibility that it may have had an entirely independent origin, 
and may never have been in the sporogonium condition. 
It 1S recognized that there are peculiar difficulties in the dis- 
ain of such a subject. Although the morphology of the 
“xisting representatives of the various groups is fairly well known, 
plas two enormous gaps in our knowledge which. make a 
biases Sr es impossible. One of these gaps is the ancient 
ape Riad the bryophyte and pteridophyte lines. For instance, 
in that the pteridophytes were well represented in the 
‘pal i ae ; : 
Paleozoic, probably even in its earliest periods. This represents 
such 
ee a tremendous stretch of time that almost any change, how- 
r 
e i . . . i 
xtensive, may have been possible'in any given form. It is 
Mo. Bot. Garden, 
1906. 
