226 Professor Lindley on the Mode of 



of a few leaves only in distant parts of the stem. The most 

 useful character to be thus derived, is when the branches regu- 

 larly bifurcate, for this kind of ratnifaction is a strong symptom 

 of cryptogamic plant, especially if accompanied by an imbricated 

 fohage. 



In Leaves, we can rarely recognise, in a fossil state, more than 

 their mode of venation, division, arrarigement, and outline, to 

 which are sometimes added their texture and surface. All 

 these are of importance, but in unequal degrees. Of the high- 

 est value is the evidence afforded by the distribution of the veins, 

 taken together with the mode of division of a leaf ; if the veins 

 are all parallel, unbranched, or only connected by little trans- 

 verse bars, and the leaves undivided, the plant was probably 

 Monocotyledonous ; and if the veins of such a leaf, instead of 

 running side by side from the base to the apex, diverge from 

 the midrib, and lose themselves in the margin, forming a close 

 series of double curves, the plant was certainly analogous to 

 what are now called Scitaminese, Marantacea^, and Musacese ; 

 but, supposing that the parallel arrangement of simple veins is 

 combined with a pinnated foliage, then the plant would proba- 

 bly have belonged to Cycadeae, that curious tribe that stands 

 on the very limits of Monocotyledons and Dicotyledons, and of 

 flowering and flowerless plants. By such characters as these 

 however, there is no means of distinguishing certain palms, if 

 /iim a fossil state, from Cycadeae. 



If veins are all of equal thickness, and dichotomous, we have 

 an indication of the Fern tribe, which is seldom deceptive. 

 Nevertheless, it must be remembered that the flabelliform 

 leaves, both of Monocotyledons and Dicotyledons, have occa- 

 sionally this kind of variation. Even if the veins are not dicho- 

 tomous, if they are all of nearly equal thickness and very fine, 

 or divided in a very simple manner, it is probable that they 

 indicate the Fern tribe, whether simple, as in the fossil genus 

 Taeniopteris, or reticulated, as in the modern genus Meniscium. 

 If veins are of obviously unequal thickness, and so branched 

 as to resemble the meshes of a net, we have a sign of Dicoty- 

 ledonous structure that seldom misleads us. 



Finally, if no veins at all are to be found, an opinion must 

 be formed, not from their absence but from other circumstances. 



