CUTICLES OF CYCADEAN EKO^'DS. 



179 



Yorkshire, indicate that the cuticular structures are not essentially affected by purely 

 local conditions, but show characters which are related to the more general conditions 

 and also to questions of phylogeny. 



More recently Prof. Nathorst (1912, p. 36) has given a short summary of the 

 results of his cuticular work, and has arranged the genera which have been studied 



&"" ^""^ & 



in five groups or orders characterised by the following forms: — (a) Tterophyllum, 

 (b) Otozamites, (c) Fseudocycas, (d) Nilssonia, (e) Ftilozamites. He does not give a 

 detailed description of the characters of the cuticles of these orders, and they appear to 

 be somewhat unequal in value. He thinks that classes (a), (b), and possibly (c), belong 

 to the Bennettitales, while (d) and (e) are more related to the modern Gymnosperms. 



Por the purposes of comparison with another group of Jurassic Gymnospcrmous 

 plants, the excellent figures of stomata of some genera of Ginkgoales given by 

 Prof. Seward * are very useful. The Ginkgoales possess a very definite and constant 

 type of stomatal structure which is somewhat similar to that found in some jSTilssonias. 



(//) Detailed Descriptions of the Cuticular Structure of some Fossil Cycadean Fronds 



I. Bennettitales. 



Ptilophyllum (Williamsonia) pecten (PhilL), n. comb. 



The large and somewhat variable group of fronds usually placed in the aggregate 

 species Williamsonia pecten, can now be divided into several sections according to the 

 structure of their epidermal cells. The smaller type of frond with regular straight linear 

 or linear-lanceolate pinnae, closely approximated and attached by almost the whole length 

 of their bases, can be distinguished from the larger type with broader pinnae, w^hich are 

 slightly falcate, more truncated at the apex and contracted at the base, and with a some- 

 what more spreading venation. So far as can be seen from external appearance, these 

 two types seem to be connected by a series of gradations, as may be noticed in the figures 

 given in Prof. Seward's * Possil Flora of the Yorkshire Coast,' where pi. 3. fig, 1 resembles 

 the small type, and pi. 3. fig. 6 probably represents a frond of the larger type (the 

 differences mentioned above are, however, much more noticeable in other examples from 

 Marske and Whitby collected by one of us). Wiien cuticular preparations are made, the 

 two types of frond can be readily distinguished by the presence or absence of large 

 numbers of thickened circular markings arranged in rows on the cuticles of the second 



O'-' ""-""O 



form. These, as mentioned later, were probably of the nature of the thickened bases or 

 scars of hairs of which no trace is seen externally without considerable magnification. 

 The fronds possessing these curious markings, as well as other slight differences, must 

 probably be placed in a new species. The separation of these two types probably involves 

 the distinction of a third and larger type of frond, and the recognition^ that the three 

 forms from Marske, figured recently by one of us (Thomas, 1913), are probably three 



* Seward (1911^), pL 4. figs. 56, 57 ; pi. 5. figs. 58-62 & 64. 



SECOND SERIES. — BOTANY, VOL. VIII. 



2e 



