ON LEPIDOPHLOIOS SCOTTII. 447 



and of that the xylem forms an outer ring 9 mm. thick (about 7 or 8 tracheides). 

 Another stem with a small pith has a wood ring 13 to 14 tracheides thick and a total 

 xylem cylinder of 3*3 mm. diameter. Generaly speaking, the innermost tracheides 

 are larger than those round the periphery, but this is not invariable, as small tracheides 

 fill in the spaces between the larger ones, even in the innermost elements of the wood. 

 The largest tracheides had a mean diameter of '16 mm. ; the smaller ones of '07 mm. 

 In length these tracheides vary greatly, as is shown in cases where pointed ends can 

 be clearly seen — indicating proximity at least to the actual terminations. One of 

 these tracheides was 5 - 5 mm. in length, while another was nearly 8 mm. The middle 

 lamella can be distinctly seen in these elements both in transverse and in longitudinal 

 sections (fig. 2, /, and fig. 2a, I). 



The peripheral layers consist of smaller and more uniform tracheides forming a con- 

 tinuous ring round the whole cylinder. The contour of the wood is fairly smooth, as the 

 protoxylem points are rounded and flat. These protoxylem teeth consist of from 9 to 

 10 tracheides, and the spaces between are each occupied by a leaf- trace bundle. The 

 elements of the protoxylem are about "02 mm. diameter, and are scalariformly thickened. 

 In no section examined can any trace of a truly spiral protoxylem element be seen. In 

 certain sections the branching of the xylem cylinder is well shown and will be referred 

 to later. 



External to the primary wood there is in most sections a thick band of almost com- 

 pletely decomposed tissue, but in one specimen this tissue is fairly well preserved. A 

 longitudinal section shows three rows of slightly elongated parenchyma abutting on the 

 wood, and this is probably the xylem sheath. Immediately outside this sheath there is 

 a zone of large-celled tissue showing signs of rupture in itself; physiologically this tissue 

 probably represents the phloem, and, wherever a branch is given off, a band of 

 the same tissue occurs on the under side, and gradually surrounds the branch bundle. 

 The leaf-traces do not give much help in describing this tissue, for in them the phloem 

 representatives cannot be distinguished from the ordinary parenchyma round the bundle, 

 except that their cells are filled with dark-coloured material. On the whole, the preser- 

 vation of the tissue in the phloem region is not sufficiently good to allow of any detailed 

 description. 



Outside the phloem is a zone of parenchyma in which all the cells appear similar 

 except the outermost layers, which are elongated tangentially. The preservation here is 

 also very poor. 



Succeeding this tissue is the middle cortex, completely preserved in one specimen 

 only (fig. 1, m.c.) ; in others merely isolated patches appear, generally surrounding 

 the outgoing leaf-trace. This tissue consists of thin-walled parenchyma with no definite 

 arrangement of its cells. There is no evidence of meristematic condition in any of these 

 cells, but in certain places they are filled with dark brown substance. It is not clear in 

 the middle cortex how these patches of cells with dark contents are arranged, but in the 

 outer cortex it can be seen that they occupy a definite position, and probably they 



