XXXIIl] CORDAITES 227 



three rather smaller secondary ribs. In a section of a leaf called 

 by Renault C. crassus 1 , a specific name used also by Lesquereux 2 

 for an impression of a leaf originally described by Goeppert as 

 Noeggerathia crassa, there are deep stereome-strands between the 

 veins next the lower epidermis alternating with single smaller 

 strands, while on the upper surface the hypodermal strands 

 occur only immediately above the veins. In a section figured 

 by Felix 3 from North Germany as C. robustus, the hypodermal 

 stereome forms continuous bands ; on the upper face the bands 

 are uniform in thickness but next the lower epidermis they form 

 a series of ribs. 



Grand' Eury's subgeneric terms Cordaites, Dory-Cordaites, and 

 Poa-Cordaites have therefore very little value as regards differences 

 in the ribbing of leaf -impressions : the large size of leaves included 

 in Dory-Cordaites and the more acute apex of the lamina as 

 compared with the obtuse apex of smaller leaves of Cordaites 

 are features of limited application and of minor importance as 

 diagnostic characters. The name Poa-Cordaites is, however, 

 usefully employed for the narrower linear leaves with an obtuse 

 apex. 



The structure of a Cordaites leaf is clearly shown in fig. 465; 

 the lamina is approximately 1 mm. thick and there are about 

 30 veins in a breadth of 2 cm. Strong I-shaped girders with the 

 webbing composed of thick-walled cells divide the mesophyll 

 into rectangular compartments : the intervening hypodermal 

 strands differ in number and size on the two faces. The epidermis 

 is not preserved : specimens of other leaves show that the stomata 4 

 occur in rows on the lower surface. The mesophyll shows no 

 differentiation into palisade and spongy parenchyma, and in 

 this respect the leaf agrees with many other forms ; but in some 

 leaves the palisade-tissue is well developed, as in C. lingulatus 

 Ren. 5 The central region of the lamina consisted of lacunar 

 tissue, portions of which are preserved, with a more compact 

 sheath of parenchyma enclosing each vein. In some leaves there 



1 Renault (79) A. PL xvi. fig. 7. * Lesquereux (78) p. 318. 



3 Felix (86) A. PI. m. fig. 1. 



4 Renault (79) A. PL xvi. fig. 11 bis; WiUs, L. (14). 



5 Renault (79) A. PL xvi. fig. -5; Stopes (03) PL ix. fig. 1; Lignier (13 2 ). 



152 



