70 



MISS NELLIE BAXCEOFT ON SOME 



fructification to "be probably tbat of W. gigas, on account of the large number of bracts 



wliicli surround it. 



Professor Seward (27, pp. 193, 194; text-fi^. 30) describes a British Museum specimen 

 of an Indian cycadean stem from the Upper Gondwana Series. This agrees very closely 

 with the stem-fragment in block I. (PI. 9. fig. 4), both externally and in anatomical struc- 

 ture {of. 27, text-fig. 30 B and PL 8. figs. 9 & 10). The fronds of Ptilophylliim cutchetise 

 (27, p. 195 ; text-fig. 32) in connection with this stem are identical with many of those 

 in the Amrapara blocks {cf. PI. 9. fig. 3). 



II. Methods of Examination oe the Blocks. 



The blocks consist of a very hard and compact porcellanous substance, the result of the 

 metamorphism by igneous rocks, of very fine close shales (19, p. 4). Tests with acid 

 showed that this " porcellanite *' is very largely, if not entirely, composed of silica, for it 

 dissolved readily in dilute hydrofluoric acid, while dilute hydrochloric acid failed to reveal 

 any trace of limy substance. 



The very complete silicification of the plant-remains enclosed in the blocks renders 

 them unsuitable for satisfactory microscopic examination in thin sections, these being 

 extremely transparent. Various attempts were made to overcome this difiiculty, such as 

 staining the sections with fuchsin ; the use of coloured screens in the condenser of the 

 microscope ; examination by polarised light and by dark ground illumination ; and the 

 examination of sections cleared of Canada balsam, and mounted in media of different 

 refraction, e.g., cedar-wood oil and water. 



None of these methods were, however, wholly satisfactory, the transparent and homo- 

 geneous nature of the material rendering impossible, in most sections, an investigation 

 of the finer anatomical details. In some cases, smooth cut surfaces were etched with 

 dilute hydrofluoric acid in the hope that this would reveal differences in the degree of 

 silicification, and thus facilitate examination by reflected light. This method also was 

 unsuccessful, for silicification and a certain amount of metamorphism due to contact wdth 

 igneous material have evidently obhterated much of the structure, and hence little 

 differentiation was apparent on the etched surfaces. 



Pinally, surfaces from which sections had been cut were treated with immersion oil 

 ■without previous etching. Such surfaces, examined by reflected light and considered 

 in conjunction with their corresponding sections, provided the means by which all 

 the evidence \vith regard to anatomical structure was obtained. 



Professor ISTathorst's collodion- film method (17) was used to elucidate the surface- 

 features of some of the leaves present in the blocks. It was determined that the cells 

 above the course of the vascular bundles are elongated and that those between are shorter 

 and more isodiametric (PL 7. fig. 10). No certain evidence wdth regard to form and 

 distribution of stomata can be obtained from a surface-film of this kind, especially if 

 the stomata are at all sunk. In this case it is possible that some apparent cell-groups 

 represent stomata-openings surrounded by epidermal cells (PI. 7. fig. 11; cf. stoma- 

 opening of Macrozamia corallines, fig. 12). 



