238 DR. A. ©. SEWARD: 
conceives as a single act may have been recurrent. It may be that we 
shall never piece together the links in the chain of life, not because the 
missing parts elude our search, but because the unfolding of terrestrial life 
in all its phases cannot be compared to a single chain. Continuity in*some 
degree there must have been, but it is conceivable that plant-life viewed as 
a whole may best be represented by separate and independent lines of 
evolution or disconnected chains which were never united, each being 
initiated by some revolution in the organic world. 
From the Triassic period to the advent of the Flowering plant Ferns were 
abundant and widely spread ; they were a prominent feature in a cycle of 
evolution which succeeded rather than sprang from the very different 
vegetation of the Palæozoic era. 
In India and other parts of the ancient continent of Gondwana Land the 
geological succession from the Permo-Carboniferous to the Triassic and 
Jurassic periods is more gradual and complete, and the conditions under 
which the strata were deposited more uniform. The southern Paleozoic 
floras are relatively poor in the variety of types as compared with the corre- 
sponding flora in the Northern Hemisphere ; their most characteristic genera 
do not oceur in the typical Permo-Carboniferous vegetation of the North. 
There is no sufficient reason at least as yet to warrant the assertion that the 
Gondwana continent was the birthplace of ferns which in the early Mesozoic 
period spread from one end of the world to the other. | 
In the Rhætic period the floras of Southern Sweden and of Tonkin were 
especially rich in certain genera of ferns, and identical or closely allied 
species flourished in both regions. Which of these two centres is nearest to 
the original home of such ferns as Dictyophyllum aud its associates? Which 
of these widely sundered areas was first occupied by the wealth of vegetation 
discovered in the rocks? To the first question there seems to be no satis- 
factory answer. While both floras are assigned to the same geological 
period it is safe to assume that they were not contemporaneous, though 
which is the older we do not know. 
There can be no doubt that the genera Matonia and Dipteris belong to a 
section of the Filicales which in former days rivalled in its geographical 
range the cosmopolitan Bracken Fern of to-day: their present restricted 
range is not an indication of relatively recent origin. Similarly the geo- 
logical record clearly establishes the fact that the other genera we have 
briefly considered, though still vigorous and widely spread, were formerly 
inhabitants of many parts of the world in which they are now unknown, 
The facts of geographical distribution must be considered together with dis- 
tribution in time : among the Ferns at least vigorous development and rapid 
spread coincide with the earlier stages of their careers, whereas restricted 
or discontinuous distribution at the present time are best interpreted as 
evidence of declining vigour or as an expression of inability to hold their 
own in competition with more recent products of evolution. 
