1858.] BUNBUEY FOSSIL LEAVES, MADEIEA. 51 



sive and careful survey of existing families of plants ; and to go 

 fiiUj into it, even if I were at present completely prepared to do so, 

 would be too great a digression from the immediate purpose of this 

 memoir. I may observe, however, that, so far as I have hitherto been 

 able to examine this subject, my conclusions are not favourable to the 

 views of the naturalists above referred to. There are but few cases, 

 as it appears to me, in which particular modifications of leaves are 

 distinctly characteristic of natural orders or of natural genera. 

 Certainly, in very many cases, wide variations in the form, venation, 

 texture, and other characters of leaves are observable in the best- 

 defined and most natural groups. For instance, in the Oaks, there 

 are at least three distinct and well-marked types of venation : — 1st, the 

 Chestnut type, in which the feathej^-veined* character is shown in the 

 highest degree, and which is exemplified in several of the Himala^'-an 

 Oaks, such as Qiiercus serrata and Q. lineata, and less perfectly in 

 some of the American kinds ; 2ndly, the Oah type proper, seen in 

 the deciduous-leaved oaks of Europe ; and 3rdly, the Laurel type, 

 in which the principal lateral veins combine into arches within the 

 margin ; this last form prevails in several of the evergreen oaks 

 both of India and of America. Again, in the small and very natural 

 genus Alnus, there are two quite distinct types of venation : — ^the 

 feather-veined, in the common Alder, and in the Alnus incana and^. 

 viridis ; the arch-veined, in the Alnus cordifolia and Alnus Nipalensis. 

 So also in the genus Fagus : our common Beech and those of North 

 America, and one of the antarctic species (jP. Antarctica), agree in a 

 well-marked type of leaf; but the Fagus Solandri of IS^ew Zealand 

 and F. betuloides of Fuegia have leaves of so different a character, 

 that their affinity to the first-mentioned species could never be 

 inferred from those organs. 



We sometimes find certain fossil leaves spoken of as having the 

 characters of the Proteaceous family. Yet, among the Proteacece 

 that I have examined, the leaves are so various in all respects, that 

 I do not know anything approaching to a common character, unless 

 it be the rigid coriaceous texture ; and this, though certainly very 

 general in the order, is scarcely apparent in some, such as Lomatia 

 dentata. What is there in common between the leaves of Leuca- 

 dendron argenteum and of Guevina Avellana ? — or of Knightia and 

 any of the Serrurias? Even in the same genus, — ^how could any 

 one, from the leaves alone, infer the generic identity of Conospermum 

 longifolium and C. er id folium'! 



The family of Rhamnece, another to which many fossil plants 

 have been referred, includes several very distinct types of venation 

 of leaves ; and, even in the genus Rhamnus itself, the leaves of 

 Rhamnus catharticus are materially different in their veining from 

 those of Rh. Frangula. 



I do not dispute that there are some families and genera of plants 

 which may be easily recognized by characters connected with the 



* See Lindley's Introduction to Botany, ed. 1., p. 93. I adopt the terms pro- 

 posed by this author for describing the venation of leaves. 



E 2 



