564 STUDIES IN FOSSIL BOTANY 



subdivide, to form the numerous bundles of the petiole. 

 In their course through the cortex, the outgoing bundles 

 are connected by cross-branches with one another, as 

 well as with other leaf-traces, and with the bundles of 

 the primary ring. 1 



In Bennettites the arrangement is a far simpler 

 one. 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 horse-shoe form, with the con- 

 cave side inwards. It then breaks up by successive 

 subdivisions into a number of smaller bundles, which 

 enter the base of the leaf (see Fig. 201, l.t.). 



In the petiole, the vascular bundles arrange them- 

 selves in an almost closed curve, slightly open and 

 involuted towards the upper surface, as is well shown 

 in tangential sections passing through the armour of 

 leaf- bases see (Fig. 200, B). 



In some Bennettiteae, as, for example, in the species 

 B. Peacliianus, from the Middle Oolite of Sutherland, 

 the pith contains several isolated rings of differentiated 

 tissue, which at first sight suggest medullary vascular 

 strands, and were at one time erroneously compared 

 with the central steles or " star-rings " of the Permian 

 Medulloseae. 2 More recent observations leave no 

 doubt that the medullary rings occurring in Bennettites 



1 See De Bary, Comparative Anatomy of Phanerogams and Ferns 

 English edition, p. 608. 



2 See above, Chapter XI. p. 441. The statement, to this effect, in 

 Solms-Laubach's Fossil Botany, p. 98, was corrected by him in his joint 

 work with Capellini, on the trunks of Italian Rennettiteae, Mem. R. 

 Accad. Sci. Bologna, vol. ii. 1S91. 



