November 3, 1892] 



NATURE 



13 



In 1890 I figured in my Memoir XVIII. (Phil. Trans. 

 1890) a transverse section of what was obviously a stem 

 of Bowmanites Dawsonz, in which the primary triangular 

 axis of the strobilus was invested by a thick zone of 

 the secondary xylem. So far as the arrangement of 

 its tissues is concerned this stem is constructed on 

 ■exactly the same plan as appears in M. Renault's and my 

 own Sphenophylla. In describing it I further said, "We 

 must unite Sphenophyllum with some forms of Astero- 

 phyllites in the same genus. It is equally clear that 

 Bowmanites, though its peculiar fructification demon- 

 strates that it constitutes a perfectly distinct genus, has 

 strongly marked features of affinity in the structure of 

 its stem to the Sphenophylloid type." 



The above reference to differences between the fructifi- 

 cation of Bowmanites and of Sphenophyllum were based 

 upon the minute description of the fruits of the latter 

 plant, published by M. Renault (" Etudes sur le Terrain 

 Houiller de Commentry," pp. 481-2). Those descriptions 

 differ widely from what exists in my Bowmanites, but M. 

 Renault distinctly identifies them with the fructification 

 of Sphenophyllum. I obtained additional and impor- 

 tant specimens of Bowmanites in 1890, which threw 

 much new light upon its organization, and which were 

 recorded in my Memoir XVIII. (Phil. Trans. 1 891). 



In July last an important communication was laid 

 before the Academy of Sciences by my friend M. Zeiller, 

 the distinguished director of the Superior National 

 School of Mines at Paris. In it he records his identi- 

 fication of a fructification of a Sphenophyllum of the 

 type of 5. pusillum of Sternberg and 5. erosutn of Lindley 

 and Hutton, with my Bowmanites Dawsoni. If this 

 determination is correct, and I see no reason for doubting 

 that it is so, we now have some more definite facts than 

 we have hitherto possessed, guiding us alike in identifying 

 the true fructification of Sphenophyllum and in deter- 

 mining its position in the vegetable kingdom. 



Before explaining M. Zeiller's observations more in 

 detail, a few words explanatory of the structure of 

 Bowmanites will make M. Zeiller's views more intelligible 

 to the reader. 



The accompanying diagram represents two nodes and 



C— 



one internode from a vertical section of this fruit, with 

 the sporangia and three sporangiophores in situ. 



So far as external contours are concerned, it is undis- 

 tinguishable from many of the true Calamarian forms of 

 fructification. It is only when cut into sections that its 

 characteristics can be discovered. Its central axis {(i) 

 has nodes [b) at short and regular intervals, and at each 

 node is a verticil of from 16 to 20 sporophylles or 

 fertile bracts {c). At their basal portions these bracts are 

 coalesced into a lenticular disk {d), from the margin of 

 which the thinner and narrowing bracts extend upwards, 



NO. I 20 1, VOL. 47] 



overlapping from two to three internodes. From the 

 upper surface of the disk numerous slender sporangio- 

 phores {e) spring, each one proceeding upwards and 

 outwards, to become attached to the upper or distal 

 extremity of a large oval sporangium (/). Each of these 

 sporangiophores has running through it a small bundle 

 of barred tracheids, which terminate at the point of 

 attachment to the sporangium. Each tracheal 

 bundle is a prolongation of one of a circle of similar ones 

 that ascend from the central axis into the disks. These 

 fructifications, besides being manifestly eusporangiate, 

 are extremely characteristic of the plant, nothing iden- 

 tical with them having been observed by any of the 

 authors who have investigated the Carboniferous strobili. 

 After these illustrations I will allow M. Zeiller to explain 

 his views in his own words. After referring to the 

 details given in my Memoir XVIII., M. Zeiller says : — 



" L'aspect de ces sporanges, ainsi attachds au bout 

 de ces pddicelles rccourbds, est exactement, \ part les 

 dimensions moindres, celui de sporocarpes de Marsilea. 

 L'analogieparait du resten'etre pas purement superficielle; 

 M. Williamson a reconnu en effet, dans le pddicelle de 

 chaque sporange, un cordon vasculaire bien caracterisd, 

 qui prouve qu'on n'a pas affaire la kune simple formation 

 dpidermique, comme pour les sporanges de Foug&res ou 

 de Lycopodindes. II faut, ace qu'il semble, regarder ces 

 pddicelles comme reprdsentant des lobes ventraux des 

 bractdes, analogues au lobe fertile des frondes d'Ophio- 

 glossdes, ou ^ ceux des Marsiliacdes ; seulement ils portent 

 k leur extrdmitd non pas une serie de sporanges comme 

 chez les premieres, ou plusieurs sores comme chez ces 

 derni^res, mais un sporange unique i paroi ioxva.it 

 d'une seule assise de cellules." 



" De cette constitution des dpis du Sphen. cuneifoliwn> 

 il report que, si les Sphenophyllum rappellent les 

 Lycopodinees par la structure de leur axe, ils s'en dloi- 

 gnent notablement par la disposition toute spdciale de 

 leur appareil fructificateur, qui tend k les rapprocher 

 plutot des Rhizocarpdes, et qu'ils doivent done bien 

 ddciddment etre considdrd comme formant une classe 

 distincte parmi les Cryptogames vasculaires."^ Agree- 

 ing thoroughly with these conclusions further comments 

 are needless. Wm. Craw^ford Williamson. 



DENDRITIC FORMS. 



'X*HE curious appearances presented by certain native 

 J- specimens of silica have been observed for so long, 

 that it is somewhat surprising that so little is known 

 about their real constitution and mode of formation. 



Rock-crystal is frequently found to contain bubbles of 

 liquid, usually either water, carbon dioxide, or petroleum, 

 or crystals, such as scales of mica, forming aventurine, and 

 fibres, such as asbestos, forming cat's-eye. More rarely, 

 however, forms of apparently vegetable origin are seen ; 

 one of the most remarkable specimens is a prolate 

 spheroid, abdut five inches long and four inches across, 

 cut from a clear colourless rock-crystal, in which are 

 embedded numerous fragments about the size of a large 

 pea, presenting the exact appearance of club-moss. 



Agate is frequently found with distinct coloured layers, 

 either flat or distorted, and usually milk-white, red, brown, 

 or black. It is then known as onyx. 



More rarely, agates are found with markings like moss 

 or foliage distributed through them ; they are then known 

 as moss-agates, or Mocha stones. 



In 1814, Dr. J. MacCulloch described some cryptogarnic 

 forms in the agates of Dunglas (Geological Trans., ii., 



'The species of Sphenophyllum to which M. Zeiller's strobili were 

 attached. 



2 Comptes Rendui des Stances de VAcadimie des Sciences, Paris, 

 July XI, 1892. 



