XVIII] BOTRYOPTERIDEAE 13 



which may be either equal or unequal (Fig. 312, ^). Secondly, it gives rise 

 to leaves of which the trace closely resembles that of an unequal dichotomy. 

 At the point of origin the trace is oval in outline, with a single external 

 pole. A little higher the presence of a few adaxial metaxylem elements 

 may indicate a relic of ancestral structure such as is seen in B. antiqiia. 

 Still higher the single protoxylem may divide into two or into three, as in 

 the tridentate petioles. In B. antiqica described by Kidston from the Petticur 

 Beds {Trans. Roy. Soc. Edin. Vol. 46, Part II, 1908) the form of the leaf- 

 trace is even more condensed, giving an oval outline with internal proto- 

 xylem ; but it becomes superficial when the 

 petiole is reached, and sometimes divides into 

 two, though not always ; so that some petioles 

 are diarch, others monarch (Fig. 314). Dr 

 Bancroft suggests that we may regard B. 

 antiqiia, cylindrica, racemosa, and hirsuta as 

 forming a series in which the foliar traces Fig- .^i4- BotryopteHs aniu/ua Kid- 



. . ston. ^, foliar trace as it leaves the 



show progl-ession from a simple structure m stem, with an internal pole of pro- 



the oldest species (B. antiqiia) to a more toxylem. ^, a foliar trace in the 



^ ^ _ ^ ^ pruiiary petiole, with the pole cup- 



complex development in the later species. In shaped at the inner boundary. px= 



It r ^i T /^ 1 i\/r i.1 protoxylem. (After Dr M. Benson, 



B. ramosa from the Lower Coal Measures the f^g,^ Bertrand.) 



tridentate type is well shown, while in B. fo- 



rensis from the French Permo-Carboniferous the most extreme development 



of the three xylem-arms is seen. The simplest trace of all, that oi B. antiqiia 



from the Petticur Beds, links readily in point of structure with what is seen 



in the simplest Osmundaceous trace. 



The peculiar "equisetoid" hairs have already been described in Vol. I, 

 p. 199, Fig. 187. It will be noted that notwithstanding their complex appear- 

 ance they are essentially simple conical hairs transversely septate. Such 

 hairs are seen in B. cylindrica with simple transverse septa, and those of 

 B.forensis may be held as a peculiar variant on that type, which is repeated 

 in the hairs of some modern Ferns, e.g. Dicksonia squamosa (see Williams, 

 Aiin. of Bot. 1925, p. 655). 



The genera Graimnatopteris and Tiihicaulis are chiefly known by their 

 stems, which bore crowded leaf-bases, and show a more complicated phyllo- 

 taxis than Botryopteris. As before, the stele is protostelic and the mono- 

 desmic leaf-trace has a simple form at first, but widens upwards into a 

 broad ribbon. In Grammatopteris, which was described by Renault from 

 the Permo-Carboniferous of Autun, each petiolar bundle appears as a 

 straight tangential band. But in Tiibicaulis, of which specimens are re- 

 corded from the Coal Measures {T. Siitcliffii Stopes), from the Permian of 

 Saxony {T. solcnites Cotta), and from the Permo-Carboniferous of Autun 

 {T. Bertieri Bertrand), the petiolar trace was shaped like a horse-shoe, 



