208 Seward. — Notes on the Geological 
might be referred to monocotyledon ous species ; Schenk 1 
points out that the wood of a Conifer, if preserved in patches, 
as frequently happens as the result of local mineralization, 
might be erroneously described as monocotyledonous. The 
close correspondence between the stems of some recent Dicoty- 
ledons and those of Monocotyledons, affords sufficient warning 
as regards the test of histological structure in identifying 
the stems of angiospermous plants. The parallel venation of 
monocotyledonous leaves is relied on much too extensively 
in the determination of fossil specimens. This form of venation 
is obviously an unsafe guide. Among Dicotyledons, such leaves 
as those of Eryngium Lassauxii , Decne., E. montana , Coult., E. 
rostratum , Car., &c., and various dicotyledonous phyllodes and 
phylloclades might be described as Monocotyledons if found 
in detached fragments 2 . The linear tapering leaves of these 
forms of Eryngium , with their marginal spines, resemble in 
a striking degree the leaves of Pandanus or certain species 
of Bromeliaceae. Among the Proteaceae 3 , of which the 
protean nature of the leaves was insisted on by Bentham 4 
and again by B unbury 5 in connexion with sources of error 
in palaeobotanical determinations, there occur leaf-forms which 
might well be referred to Monocotyledons. On the other 
hand, a comparison of the leaves of certain species of Smilax 
with the genera Pleroma or Cinnamomum , not to mention other 
examples, shows the danger of following too closely venation- 
characters. Lindley gave expression to this dicotyledonous 
form of venation among Monocotyledons by the institution 
of the family of Dictyogens 6 . The leaves of Agathis, certain 
forms of Podocarpus (section Nageia ), and detached pinnae of 
Cycadean fronds, may be quoted as possible sources of error 
where venation is accepted as the most important test. 
1 Die fossilen Pflanzen (Schenk’s Handbuch, Vol. iv, 1890), p. 200. 
2 Cf. Drude, in Schenk’s Handbuch, Vol. iii (ii), p. 304; see also Henslow in 
Journ. Linn. Soc. Vol. xxix, 1893, p. 485. 
3 My thanks are due to Mr. Rendle, of the British Museum, for calling my 
attention to some of the less known forms in this family. 
4 Annual Address, Linn. Soc., 1870, p. 13. 5 Botanical Fragments, p. 310. 
6 The Vegetable Kingdom, 1846, p. 21 1. 
