CALAMARIEAE. 299 



the outside in the secondary wood, that is they become indistinguishable 

 there, while in Calamodendron they retain their breadth and distinctness 

 throughout. The wood of Arthropitys is nearly uniform, that of the 

 other genus is composed of alternating ribbon-like bands of nearly equal 

 breadth, some of which represent the wedges of the bundle, the others the 

 rays. There is a difference also in the vertical distribution of the two types. 

 Arthropitys is found in various horizons of the true Coal-measures from 

 the base upwards, being extremely abundant in the Coal-measures of 

 Lancashire, in which no trace of Calamodendron has hitherto been found. 

 In fact the latter genus seems to be confined to the uppermost beds of the 

 Carboniferous formation and to the Rothliegende, in which it has been 

 shown to occur associated with Arthropitys at Chemnitz and Autun, in the 

 Val d'Ajol and at Grand' Croix. The specimens from Grand' Croix are 

 black throughout ; in those of Chemnitz, figured first by Cotta l , the bands 

 in the transverse section are alternately lighter and darker in colour, and 

 the whole has thus a pretty and highly characteristic appearance. 



Detailed accounts of the peculiar composition of the medullary rays in 

 Calamodendron are not frequent either in Unger 2 , Petzholdt 3 , or Renault 4 . 

 According to the latter author they consist chiefly of elongated thick-walled 

 fibres. Either each ray consists of two fibrous laminae which are separated 

 by an intervening band of parenchyma and adjoin the bundles, or of five* 

 successive laminae, the lateral and central laminae being composed of fibres, 

 the two between them of parenchyma. The account given by Unger, who 

 examined the specimens from Chemnitz only, while Renault relies on those 

 from Autun and Grand' Croix, is somewhat different. He says that the 

 wood consists of alternating bands of different structure. Both these bands 

 contain ordinary parenchymatous medullary rays which may be formed of 

 several rows of cells, but in some of them the mass of the wood consists of 

 scalariform vessels, in the others entirely of parenchyma-cells of narrow 

 diameter and with strongly thickened walls. But the figure of a tangential 

 section given in Petzholdt 5 does not answer to this description, but agrees 

 rather with Renault's account. In specimens from Grand' Croix I find the 

 structure to correspond exactly with Renault's description. A specimen 

 from Chemnitz on the other hand shows an entirely different structure, and 

 agrees to some extent with Unger's description. In the former the primary 

 ray consists of two lateral laminae of fibres with a narrow band of paren- 

 chyma interposed between them ; in the latter of" a compact fibrous, not, as 

 Unger supposes, a parenchymatous mass, which encloses numerous rays of 

 moderate depth and varying breadth. We should in the latter case in fact 

 be more correct if we spoke of an interfascicular wood rather than of a 



1 Cotta (1). 2 Unger (9). 3 Petzholdt (1), with figure. 4 Renault (15). 



3 Petzholdt (1), t. 8, f. 4. 



