REMAINS OF STEMS OF DOUBTFUL AFFINITY, ETC. 357 



there is a primary bundle with an initial strand towards the outside. The 

 bundle consists of pitted and scalariform tracheides. In the secondary 

 wood there are only pitted tracheides ; and these have the bordered pits, 

 which are crowded together as in Araucaroxylon and flattened into a 

 polygonal shape, only on the radial surfaces. The secondary bast-region 

 in Poroxylon Boysseti is homogeneous, in P. Edwardsii l it contains sieve- 

 tubes with a broad lumen, which are said to resemble those of Encephalartos. 

 Outside it is the thick parenchymatous rind containing a large number 

 of hypodermal fibre-strands with a radially elongated transverse section. 

 Bark is formed according to Bertrand and Renault in Poroxylon Edwardsii ; 

 and in this process the first layer of periderm is developed on the inner 

 border of the primary rind. The succeeding layers arise in the bast and 

 cut out flat scales of bark from beneath. The preliminary communication 

 of the two authors already mentioned contains further important anatomico- 

 morphological data, from which I select the following. The phyllotaxy 

 is T 5 s and the leaf-trace is formed of a single strand. There are lateral 

 buds in the axils of the leaves, but they are not always developed. Un- 

 fortunately nothing is said about the leaves themselves. But Renault 2 

 has found fragments of leaf-stalks associated with the stems of Poroxylon 

 in the pebbles of Autun, which he inclines to refer to this group on account 

 of their great resemblance to the stems. He says on this point in his 

 Memoir 3 : ' Their structure is so like that of the branches, that there 

 can be no doubt of their connection.' They show first of all on the 

 elliptical transverse section exactly the same short radial hypodermal 

 strengthening ribs mentioned above. In the middle of their stout thick 

 parenchyma, which is marked throughout with isolated dark points, lies 

 a much-expanded vascular bundle which is divided by medullary rays 

 into several segments lying beside one another. The bundle consists 

 of an upper portion of wood, and an under portion of the same to 

 which the bast-layer is attached. The whole gives the impression that 

 secondary growth must have taken place. The upper wood-portion, 

 which in that case would answer to the primary bundle of the stem, is 

 traversed by tracheides without regular arrangement, the scalariform 

 elements being beneath, the pitted above. In the lower portion the 

 pitted tracheides form straight parallel rows, as is usually the case in 

 secondary wood. If all these statements are confirmed, there is not 

 much to be said against placing these two species of Poroxylon with 

 Cycadeae. Still they would differ from our recent forms in the important 

 point, that the trace-bundles maintain the anomalous position of their 

 initial strand on the outer side of the bundle even in the stem. 



1 Renault (2), t. 16, f. i. 3 Renault (1), t. 13, f. u, and (2), vol. i, t. 16, f. 8. 



3 Bertrand et Renault (3), p. 120. 



