52 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [^pr* 28, 



leaves and their appendages. Such are the Myrtacece*, the Mela- 

 stomacece, the Coniferce, the Rubiacece ( Cinchonacece of Lindley), the 

 genera Nepenthes, Sarracenia, Bauhinia, Begonia, Cinnamomum, 

 and to a certain extent the genus Ficusf. But every botanist who 

 has examined large unarranged collections of dried plants from 

 foreign countries must be aware how difficult it is, in general, to 

 make out the affinities of specimens without fruit or flower, and 

 how often very similar leaves belong to plants of widely different 

 families. This part of the subject has, in truth, been so ably 

 treated by Dr. Hooker in the 10th volume of this Society's Journal, 

 p. 163-165, that it would hardly have been necessary to touch 

 upon it again, were not the confidence with which some eminent 

 foreign geologists assign generic names to mere detached leaves 

 calculated, in my opinion, to mislead the inexperienced ; wherefore 

 I have thought it advisable to enter a fresh protest, and to remind 

 geologists of the uncertainty of the evidence we possess. 



The imperfect state of our materials must always be borne in 

 mind. "When we have before us only detached leaves, as most 

 commonly happens in fossiliferous deposits, and as is the case, in 

 particular, with all the specimens I have seen from Madeira, we 

 lose the benefit of several characters which assist materially in the 

 determination of recent plants : in particular, the character of 

 insertion (alternate, opposite, or whorled) ; and the more important 

 one of the presence or absence of stipules, and their nature when 

 present. As an example of the importance of these organs, I may 

 notice, that the Magnolia family may be easily known, in general, 

 by the peculiarities of the stipules, taken together with those of the 

 leaves ; but the leaves separately would afford no sufficient indica- 

 tion of the order. The same may be said, still more decidedly, of 

 the Cinchonacece of Lindley. 



Another character, of great use in the determination of recent 

 plants, but almost necessarily wanting in the fossil state, is the 

 nature of the pubescence, — the hair, down, scales, or other clothing 

 of the surface. 



In those rare cases where the fossil leaves are so weU. preserved 

 that the cellular structure of the epidermis, and its pores or 

 stomata, can be satisfactorily examined, these may probably afford 

 valuable aid towards the determination of affinities. Yet it is a 

 point by no means determined, and one which deserves careful 

 study in recent plants, how far the characters afforded by the 

 epidermis and its pores are in accordance with those of other organs. 

 It is certain, to mention one instance only, that the structure of the 

 epidermis and position of the stomata in Salisburia are exceptional 

 in the family of Coniferce. 



In all that I have said, I have been speaking of the difficulty of 

 determining plants by their leaves only. Where fruits of a marked 



* The peculiar intramarginal vein of Myrtacecs, however, occurs in several 

 species of other families. 



t I purposely omit to mention those genera wliich consist of only one species, 

 such as lAriodendron. 



