.54 DESCRIPTIVE CATAI.oMI. 



the cortex the big leaf-traces with their fan of secondary 

 tissues pass out directly to the leaf-bases, and do not encircle 

 the stem in their way out as is the case in living Cycads. Scott 

 describes their course as follows (1909, p. 564) : "A single 

 bundle leaves the ring, starting from the lower angle of one of 

 the meshes, which (as shown in tangential section) are occupied 

 by the primary medullary rays. As the leaf-trace passes out- 

 through the cortex it assumes a horseshoe form, with the com 

 side inwards. It then breaks up by successive subdivisions into 

 a number of smaller bundles, which enter the base of the lent 1 . 



Text-fig. 10. Bctnirttift't (iih< <':irr. Trap- 'tion of pnrt 



of the phloem, showing the regular alternation of thick- uiul thin- 

 walled elements, m., the broad medullai y ray cell?. 



In the petiole the vascular bundles arrange themselves in an 

 almost closed curve, slightly open and involuted towards tin- 

 upper surface, as is well shown in tangential sections passing 

 through the armour of leaf-bases " (see text-fig. 8). 



The massive leaf-basts are well shown in this fossil. According 

 to Carruthers (1870, p. 700), they account for 4 inches (10 cm.) 

 of the thickness of the trunk. They measure tungeiitiully from 

 3-4 cm. and vertically 2-2-5 cm. They are mainly composed 

 of a large-celled ground-tissue, through which run innumerable 

 gum-canals. At. their edge there appears to be something in the 



