CONIFERS. 189 



Examples of heterophylly have been recorded among fossil forms 

 e.g., Voltzia, heterophylla, Brong., 1 from the Bunter beds; and the 

 specimens of Sequoia Tournalii (Brong.), figured by Gardner 2 from 

 the Bagshot beds of Bournemouth, show a considerable difference 

 in the form of the leaves. The microscopical examination of the 

 epidermal cell-outlines of fossil coniferous leaves has been success- 

 fully adopted in some instances, e.g. by Zeiller 3 in the case of 

 Frenelopsis Hoheneggeri (Ett.), and by Schenk 4 in several instances. 



In addition to the similarity of leaf form in different species and 

 genera, and the heterophylly in the same species, it is important 

 to note the common occurrence of more than one method of leaf 

 arrangement in the same tree. Masters, 5 in his useful paper in 

 the Journal of the Linnean Society for 1891, has drawn attention to 

 this variation in leaf arrangement among recent species of conifers. 



In describing cycadean flowers, it was pointed out how difficult 

 it is in some cases to distinguish between the cones of cycads and 

 those of certain genera of conifers, when we have only external 

 form to guide us. The seeds of Cephalotaxus, Ginkgo, Torreya, and 

 other genera may be easily mistaken for those of Cycas and other 

 cycads. There is in many instances, the same difficulty in identifying 

 the detached cones of recent conifers as in determining detached 

 leafy twigs. Schimper and Mougeot, recognizing the difficulty of 

 discriminating between fossil cones, suggested the general generic 

 term Strobilifes, 5 which they used in a somewhat similar sense to 

 that in which I have used the more comprehensive genus Conites. 



Hitherto the number of Conifera recorded from English Wealden 

 strata has been extremely small. In addition to isolated cones 

 described by Carruthers, Gardner, and others, we have only one 

 species represented by a leaf-bearing branch Sphenolepidium Kur- 

 rianum (Dunk.). The Rufford Collection has enabled us to recognize 

 as British plants several of the species previously described from 

 Germany and elsewhere, and to make several additions to the list 

 of Wealden Coniferce. 



1 Brongniart (o), p. 451. See also Schimper and Mougeot, p. 22, pis. vi.-xiv. 



2 Gardner (2), pi. v. 



3 Zeiller (3), p. 231, pi. xi. 



4 Schenk (A. 1), Fl. foss. Grenz. Keup. Lias, and (A. 2) Palteontographica, 

 vol. xix. 



5 Masters, p. 244. 



6 Schimper and Mougeot, p. 31. 



