XV] LEPIDOSTROBUS 189 



of Lepidodendron Harcourtii. In shape and in the main 

 morphological features this type resembles L. variabilis, which 

 is however known only in the form of casts and impressions. 

 A cone of L. oldhamius, 2 — 3 cm. in diameter, possesses a 

 medullated stele consisting of a ring of primary xylem (fig. 

 191, D, x) with exarch protoxylem and no secondary elements. 

 Maslen found several short tracheae at the periphery of the 

 xylem and states that these led him to compare the cone with the 

 vegetative shoots of Lepidodendron vasculare, but the common 

 occurrence of such elements in different types of shoot renders 

 them of little or no specific value. The inner cortex is like 

 that of vegetative shoots of Lepidodendron and the middle 

 cortex, which was no doubt of the type described in Lepido- 

 strobus Brownii, is represented by a gap in the sections, beyond 

 which is the stronger outer cortex (fig. 191, D) passing into the 

 horizontal pedicels of the sporophylls. The section of the axis 

 reproduced in fig. 191, D, was figured by Binney^ as Lepido- 

 dendron vasculare. The leaf-traces, several of which are seen 

 in the middle cortical region in fig. D, It, consist of a strand 

 of scalariform tracheae, with a mesarch protoxylem, succeeded 

 by a few parenchymatous cells ; beyond these there is usually 

 a small gap which was originally occupied by a strand of thin- 

 walled cells. It is important to note that in one sporophyll- 

 trace figured by Maslen'' there is a strand of thin- walled 

 elongated elements abutting on the xylem, which he describes 

 as phloem. This tissue is certainly more like true phloem than 

 any which has hitherto been described in the leaf-traces of 

 vegetative shoots. The state of preservation is not, however, 

 sufficiently good to enable us to recognise undoubted phloem 

 features. 



In such cones as I have examined no tissue has been seen 

 which shows the histological features characteristic of the 

 secretory zone of vegetative shoots: the "phloem" (Maslen) 

 occupies the position in the sporophyll bundle which in the 

 vascular bundles of foliage leaves is occupied by a dark-celled 

 and partially disorganised tissue in continuity with the secre- 

 tory zone of the main stele. It may be that in the strobili 



1 Binney (71) PI. Tin. figs. 2, 4. "' Maslen (99) PI. xxxvi. fig. 11. 



