X] PITH-CASTS OF CALAMITES. 365 



Older stems {transverse sections) 15-17, 62, 77-87, 115 «, 117* 118*, 



120, 122*-124* 1933 a, 1934, 1941. 

 {Tangential sections) 20, 24, 26, 37, 38, 49, 90, 91, 130, 138, 1937, 



1943. 

 {Radial sections) 20, 20 a, 21, 22, 48, 65-68, 83-91, 137* 138* 1937. 

 (ii. Arthrodendron) 36, 37, 38, 52, 54. 

 Roots. 1335, 1347, 1350, 1356. 



Strohili. i. Calamostachys Binneyana. 991, 996, 997, 1000, 1003, 1005, 

 1007, 1008, 1011, 1013, 1016, 1017, 1022, 1023, 1037 a, 1043. 

 ii. C. Casheana. 1024, 1025, 1587, 1588. 

 iii. Palaeostachya vera. 110, 1564, 1567, 1569, 1579, 1583.] 



III. Pith-casts of Calamites. 



A. Calamitina. B. Stylocalamites. C. Eucalamites. 



Palaeobotanical literature contains a large number of species 

 of Calamites founded on pith-casts alone. Many of these so- 

 called species are of little or no value botanically, but while we 

 may- admit the futility of attempting to recognise specific types 

 in the same sense as in the determination of recent plants, it is 

 necessary to pay attention to such characters as are likely to 

 prove of value for descriptive and comparative purposes. From 

 the nature of the specimens it is clear that many of the 

 differences may be such as are likely to be met with in 

 different branches of the same species, while in others the 

 pith-casts of distinct species or genera may be almost identical. 



The most striking differences observable in Calamite casts 

 are in the character of the intemodes, the infranodal canals, 

 the number and disposition of branch-scars, and other surface 

 features. Occasionally it is possible to recognise certain ana- 

 tomical characters in the coaly layer which often surrounds a 

 shale- or sandstone-cast, and the surface of a well preserved cast 

 may give a clue to the nature of the wood in the faint outlines 

 of cells which can sometimes be detected on the cast itself*. 

 The breadth of the carbonaceous envelope on a cast has been 

 frequently relied on by some writers as an important character. 

 It has been suggested ^ that we may arrive at the original 

 thickness of the wood of a stem by measuring the coaly layer 

 1 Zeiller (88), PI. liv. fig. 4. « Stur (87), p. 17. 



