240 LYCOPODIALES [fH. 



Anatomy. 



The more important anatomical features of Stigmaria must 

 be dealt with briefly. Williamson's monograph, published in 

 1887^, is considerably in advance of the work of that of any of 

 the numerous writers who had previously dealt with the 

 subject. The diagrammatic transverse section reproduced in fig. 

 210, H, illustrates the general arrangement of the tissues. The 

 meduUated stele was described by Williamson as consisting 

 entirely of centrifugally developed secondary xylem and 

 distinguished, therefore, from the stele of a Lepidodendron or 

 Sigillaria by the absence of a centripetally produced primary 

 xylem zone. The secondary xylem tracheae are characterised 

 by scalariform pits on both radial and tangential walls and, as 

 shown in a figure given by Solms-Laubach^, the spaces between 

 the transverse bars are bridged across by fine threads, as in 

 the tracheae of Lepidodendron. 



One of the largest specimens of a petrified Stigmaria which 

 I have seen is one lent to me by Mr Lomax from the Coal- 

 Measures of Halifax in which the flattened transverse section 

 measures 18 cm. x 3'5 cm., the cylinder of wood being I'l cm. x 

 7 mm. in diameter. 



In French examples of Stigmaria or Stigmariopsis it has 

 been demonstrated by Renault^ that primary xylem strands 

 occur very like those in the stem of some species of Sigillariae 

 (see p. 219). If a well-preserved section of an English Stigmaria 

 is examined it will be seen that the edge of the secondary wood 

 consists of a few narrower elements which do not exhibit the 

 radial seriation characteristic of secondary elements. 



A type of Stigmaria characterised by centripetal primary 

 wood has been described by Weiss* and referred by him to 

 Bothrodendron m,undum; the main results of his observations are 

 stated in the account of Bothrodendron on a subsequent page. 

 This discovery is of considerable interest not only as rendering 

 our knowledge of Bothrodendron remarkably complete but as 

 confirmatory of Renault's account of French Stigmarian axes in 



1 Williamson (87) A. 2 Solms-Laubach (92). 



3 Benault (96) A. PL xl. fig. 5. « Weiss, F. E. (08). 



