X] WILLIAMSON. ijQl 



Calamitea bistriata\ Goppert rightly decided that the plants so 

 named by Cotta differed in important histological characters 

 from other species of Calamitea. The generic name Arthro- 

 pitys has been widely adopted for a type of Calamitean stem 

 characterised by definite structural features. The great ma- 

 jority of the petrified Calamite stems found in the English 

 Coal-Measures belong to Goppert 's Arthropitys. 



The next proposal to be noticed is one by Williamson- in 

 1868 ; he instituted the generic name Calamopitys for a few 

 examples of English stems, which differed in the structure of 

 the wood and primary medullary rays from previously recijrded 

 types. We have thus four names which all stand for generic 

 types of Calamitean stems. Of these Galamodendron and 

 Arthropitys are still used as convenient designations for stems 

 with well-defined anatomical characters. The genus Calamitea 

 is no longer in use, and Williamson's name Calamopitys had 

 previously been made use of by linger^ for plants which do not 

 belong to the Calamarieae. As it is convenient to have some 

 term to apply to such stems as those which Williamson ujade 

 the type of Calamopitys, the name Arthrodendron is suggested 

 by my friend Dr Scott ^ as a substitute for Williamson's genus. 



The twofold division of the Calamites instituted by Bron- 

 gniart has already been alluded to, and for many years it was 

 generally agreed that both Pteridophytes and Gymnosperms 

 were represented among the Palaeozoic fossils known as Cala- 

 mites. The work of Prof. Williamson was largely instrumental 

 in proving the unsound basis for this artificial separation ; he 

 insisted on the inclusion of all Calamites in the Vascular Cryp- 

 togams, irrespective of the presence or absence of secondary 

 wood. By degrees the adherents of Brongniart's views 

 acknowledged the force pf the English botanist's contention. 

 It is one of the many signs of the value of Williamson's work 

 that there is now almost complete accord among palaeo- 

 botanical writers as to the affinities of Calamitean plants. 



1 The original specimens described by Goppert are in the rich palaeobotanical 

 Collection of the Breslau Museum. 

 - Williamson (7P), P- 174. 

 -^ vide Solms-Laubach (96). * Letter, November 1897. 



