XXll FLOKA 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 Lycopodiacece, and 

 a number of other Orders and Genera, as low as those now living, existed at that time also. 



Another point is the evidence, t 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 Araucarice, 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 palaeontology, 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 

 of continents. 



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 Palfeozoic period still exist, and therefore have as famiiidS "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 thv. 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 Gymnosperinous 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 in vegetable impregnation and embryogeny into the service of classification, the long- 

 established facts regarding the development of the stem, flower, and reproductive organs themselves of Gym- 

 nospermous plants have been relatively underrated or wholly lost sight of; and if an examination of the doctrines 

 of 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 first foot-note of p. xxi (*) : 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. 



