22 LEAVES OF LIRIODENDRON — HOLM, 



other plants, as for iustance, species of Acer and Aralia, especially if 

 the palmate nervation of these is not to be seen distinctly, which a 

 small part of a lobe might not be able to show. And as to the smaller 

 leaves, the obcordate ones, these are, when they occur as fossils, even 

 more misleadiug. Leaves with the apex emarginate and of an obcordate 

 form occur so often in the other families as the only typical form of the 

 leaf or leaflet, that it would be more natural for the paleobotanist to 

 think of such families rather than of such a genus as the Liriodendron. 

 And their nervation is, in proportion to their size, rather indistinct and 

 far from characteristic; they are regularly feather-veiued. 



But, still, as will be shown later, several fossil leaves of this obcor- 

 date shai)e have been identified as belonging to Liriodendron, whether 

 correctly or not is another question, but why should the ancient types 

 not show at least a similar kind of variation, as does the recent one? 

 There is a peculiar circumstance connected with Dr. Newberry's Liri- 

 odendron oblongifoUum, L. quercifolium, and L. simplex {I. c.). As the 

 author remarks, the leaves of these three species are proportionally 

 longer than those of the recent species. This seems to be characteristic 

 of several of the other ancient forms, and is a point of great interest, 

 especially because I believe, we may trace it in the recent leaf. There 

 is, namely, in the leaf of Liriodendron Tulipifera a short point in the 

 middle of the notch which is an elongation of the midrib, and 1 have 

 observed this feature in all the leaves 1 have examined, of both old 

 and young trees. This prolongation of the midrib might then show a 

 rudiment of a longer midrib, that is, the leaf may formerly have been 

 longer and then for some reason have decreased to its present size. It 

 might, however, be objected to this supposition that it very often oc- 

 curs, that such a point is to be found in leaves, and especially very 

 commonly in the obcordate leaflets of many Leguniinosw, where we are 

 not entitled to presume a reduction in length of the leaf. I am w^ell 

 aware of this, but there is another fact that must be considered, 

 namel}^, that the nervation of the leaflets, pointed and obcordate or 

 with the apex of the blade notched as in Liriodendron, in Hcvmatoxylon, 

 Coluiea, and others, is somewhat different from that of such forms 

 of the recent Tulip-tree. For even if the Liriodendron-lGcixas and the 

 Leguminosceleahets are feather-veined, and generally show the same 

 relatively coarse reticulation, yet while the nerves of the Legnminoscv 

 leaflets are almost parallel to each other, this is not always the case with 

 Liriodendron. Just beneath the upper margin of the leaf oH Lirioden- 

 dron Tulipifera is to be observed one pair of very short and rather 

 indistinct ribs, and these proceed almost horizontally from the midrib, 

 while the other ones, at least in the smaller leaves, form an acute angle 

 with the midrib. Might this pair of ribs not have shown an additional 

 pair of lobes, when the leaf was longer, and are they not to be supposed 

 to have always been present in the elongated midrib? This would at 

 le.ist be a great help to the correct understanding of the long leaves 



