XXll FLORA OF TASMANIA. 
should not only be the highest now existing, but have more highly differentiated vegetative organs 
than any subsequently appearing ; and that the dicotyledonous embryo and perfect exogenous wood 
with the highest specialized tissue known (the coniferous, with glandular tissue*), should have pre- 
ceded the monocotyledonous embryo and endogenous wood in date of appearance on the globe, are 
facts wholly opposed to the doctrine of progression, and they can only be set aside on the supposition 
that they are fragmentary evidence of a time further removed from that of the origin of vegetation 
than from the present day ; to which must be added the supposition that types of Lycopodiacea, and 
a number of other Orders and Genera, as low as those now living, existed at that time also. 
Another point is the evidence^ said to be established, of genera now respectively considered pecu- 
liar to the five continents having existed cotemporaneously at a comparatively recent geological epoch 
in Europe, and the very close affinity, if not identity, of some of these with existing species. The 
changes in the level and contour of the different parts of the earth's surface which have occurred 
since the period of the chalk, or even since that preceding the rise of the Alps, imply a very great 
amount of difference between the past and present relations of sea and land and climate ; and it is 
no doubt owing to these changes that the Araucaria, which once inhabited England, are no longer 
found in the northern hemisphere, and that the Australian genera which inhabited Europe at a period 
preceding the rise of the Alps have since been expelled. 
Such facts, standing at the threshold of our knowledge of vegetable paleontology, should lead 
us to expect that the problem of distribution is an infinitely complicated one, and suggest the idea 
that the mutations of the surface of our planet, which replace continents by oceans, and plains by 
mountains, may be insignificant measures of time when compared with the duration of some existing 
genera and perhaps species of plants, for some of these appear to have outlived the slow submersion 
35. From the sum then of our theories, as arranged in accordance with ascertained facts, we 
may make the following assumptions :— That the principal recognized families of plants which inha- 
bited the globe at and since the Paleozoic period still exist, and therefore have as families survived 
all intervening geological changes. That of these types some have been transferred, or have migrated, 
from one hemisphere to another. That it is not unreasonable to suppose that further evidence may 
be forthcoming which will show that all existing species may have descended genealogically from 
fewer pre-existing ones; that we owe their different forms to the variation of individuals, and the 
power of limiting them into genera and species to the destruction of some of these varieties, etc., and 
the increase in individuals of others. Lastly, that the fact of species being with so much uniformity 
the ultimate and most definable group (the leaves as it were of the family tree), may possibly be 
owing to the tendency to vary being checked, partly by the ample opportunities each brood of a 
* The vexed question of the true position of Gymnospermous plants in the Natural System assumes a some- 
what different aspect under the view of species being created by progressive evolution. In the haste to press the 
recent important discoveries iu vegetable impregnation and embryogeny into the service of classification the W- 
estabbshed facts regarding the development of the stem, flower, and reproductive organs themselves' of G V m- 
nospermous plants have been relatively underrated or wholly lost sight of; and if an examination of the doctrines 
ot progression and variation lead to a better general estimation of the comparative value of the characters presented 
by these organs, the acceptance or rejection of the doctrines themselves is, in the present state of science, a matter 
of secondary importance. 
t See . M foot-note of p. xx i (*) : what I have there said of the supposed identifications of the Australian 
genera applies to many of those of the other enumerated quarters of the globe. 
