LEPIDOSTROBUS 177 



the axis is occupied by a small stele, in which a ring 

 of primary wood surrounds the pith. In the wood the 

 larger elements, which have a scalariform thickening, 

 are towards the interior ; the outer margin is produced 

 into a number of somewhat prominent points, and 

 here the narrow spiral elements of the protoxylem are 

 found ; thus the development of the wood was evidently 

 centripetal, as in the vegetative stem. In exceptionally 

 well-preserved specimens, the phloem-zone, surrounding 

 the wood, is preserved ; this zone is largely parenchy- 

 matous, the elongated elements, presumably forming 

 the true phloem, occupying only a small space. From 

 some of the best-preserved specimens, it appears that 

 the tissue next the wood was entirely parenchymatous, 

 while the true phloem lay more to the exterior. In 

 Lepidostrobus Brownii, the structure of which is better 

 preserved than that of L. oldhamius, a distinct endo- 

 dermis, separating the stele from the inner cortex, can 

 be traced. 



The inner and outer zones of the cortex are usually 

 well preserved in L. oldhamius, while the intermediate 

 region has perished — a common condition in the stems 

 of fossil Lycopods. The inner cortex consists of a 

 narrow zone of parenchymatous tissue ; beyond this 

 is the gap representing the position of the wide middle 

 cortex ; the outer cortical zone is usually perfect, and 

 consists of thick -celled tissue, largely made up of 

 fibrous elements. This zone is continuous on the 

 exterior with the bases of the sporophylls. 



The leaf-trace strands, one of which runs out to 

 each sporophyll, have a very steep course, so that a 

 large number, corresponding to several circuits of the 



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