548 
sporophyte have been derived by a process 
of sterilization, and that the transformation 
of sporophylls to foliage leaves in an indi- 
vidual indicates the mode of progress in 
this sterilization, does not necessarily in- 
volve the idea that the sporophyll of any of 
the ferns, as they now exist, was the primary 
form of the leaf in that species, and that 
by sterilization of some of the sporophylls, 
the present dimorphic form of the leaves 
was brought about. The process of the 
evolution of the leaf has probably been a 
gradual one and extends back to some an- 
cestral form now totally unknown. One 
might differ from Professor Bower in the 
examples selected by him to illustrate the 
course of progress from a simple and slightly 
differentiated sporophyte to that exhibited 
in the various groups of the Pteridophyta, 
but it seems to me that he is right in so far 
as his contention for the evolution of vege- 
tative and assimilatory members of the 
sporophyte can be illustrated by a compar- 
ison of the different degrees of complexity 
represented by it in different groups, and 
that this illustrates the mode of progress, as 
he terms it, in the sterilization of potential 
sporangenous tissue. 
On this point it appears that Professor 
Bower has been unjustly criticised. The 
forms selected to illustrate his theory were 
chosen not to represent ancestral forms, or 
direct phylogenetic lines, but solely for the 
purpose of illustrating the gradual transfer- 
ence of spore-bearing tissue from a central 
to a peripheral position, and the gradual 
eruption and separation of spore-bearing 
areas, with the final sterilization of some 
of these outgrowths. 
To maintain that in phylogeny the sporo- 
phyllis a transformed foliage leaf would ne- 
cessitate the predication of ancestral plants 
with only foliage leaves, and that in the 
case of these plants the vegetative condi- 
tion of the sporophyte was the primary one, 
spore production being a later developed 
SCIENCE. 
[N. 8. Von. VI. No. 145. 
function. Of the forms below the Pterido- 
phyta, so far as our present evidence goes, 
the sporophyte originated through what 
Bower calls the gradual elaboration of the 
zygote. All through the Bryophyta, wher- 
ever a sporophyte is developed, spore pro- 
duction constantly recurs in each cycle of 
the development, and yet there is no indi- 
eation of any foliar organs on the sporo- 
phyte. The simplest forms of the sporo- 
phyte contain no assimilatory tissue, but in 
the more complex forms assimilatory tissue 
is developed to some extent, showing that 
the correlative forces which formerly were 
so balanced as to confine the vegetative 
growth to the gametophyte, and fruiting to 
the sporophyte, are later changing; that 
vegetative growth and assimilation are 
being transferred to the sporophyte, while 
the latter still retains the function of spore 
production, though postponed in the ontog- 
eny of the plant. 
If we cannot accept some such theory for 
the origin of sporophylls and foliage leaves 
by gradual changes in potentially sporoge- 
nous tissue somewhat on the lines indicated 
by Bower, it seems to me it would be nec- 
essary, as already suggested, to predicate an 
ancestral form for the Pteridophyta in 
which spore production was absent. That 
is, spore production, in the sporophyte of 
ancestral forms of the Pteridophyta, may 
never have existed in the early period of its 
evolution and spore production may have 
been a later development. But this, judg- 
ing from the evidence which we have, is im- 
probable, since the gametophyte alone 
would then be concerned in transmitting 
hereditary characters, unless the sporophyte 
through a long period developed the game- 
tophyte stage through apospory. Bower 
says in taking issue with Goebel’s state- 
ment that the experiments on Onoclea 
prove the sporophyll to be a transformed 
foliage leaf: “I assert, on the other hand, 
that this is not proved, and that a good 
