684 



NATURE 



[July 29, 1920 



ray of the stellate xylem, a fact that confirms 

 the Lycopod comparison (Fig-. 4). Longitudinal 



cortex of stem and rhizome often contain fungal 

 hyphae. It is possible that in the rhizome these 



Photo\ [Dr. Kidslon. 



Fig. 4.— Large stem of Asteroxylon cut transversely just below a dichotomy, and showing leaves attached externally (X about lo). 



sections show the relations of epidermis, cortex, 

 phloem and xylem, and the way in which the inner 



Photo\ [Dr. Kidston. 



Fig. 5. — Stoma of Asteroxylon Mackiei in surface view { X 210). 



NO. 2648, VOL. 105] 



may have been concerned in mycosliric nutrition. 

 Higher powers demonstrate the tracheides as 

 irregularly, or spirally, barred, but not scalari- 

 form. An endodermis has been seen delimiting 

 the cylindrical stele, and mesarch protoxylem is 

 found in the xylem-rays. The leaves are paren- 

 chymatous, the vascular strands stopping- short 

 at their bases. The epidermis has been found 

 to bear very perfect stomata (Fig. 5). The 

 essential points of structure of the plant are thus 

 fully known. 



In certain blocks sporangia have been found 

 attached to profusely dichotomising stalks of 

 simpler structure than the main stems of Astero- 

 xylon, and not definitely attached to them. They 

 are associated, however, with stems of Astero- 

 xylon, while those of Hornea and Rhynia, from 

 which they are structurally distinct, are absent 

 from the blocks. The association makes it prob- 

 able that these peculiarly forked branches and 

 sporangia really belong to Asteroxylon. The 

 sporangia are relatively small and pear-shaped, 

 and they had a distal dehiscence. The whole 

 plant of Asteroxylon was thus more advanced in 

 various respects than any of the other three plants 

 of the chert. 



[To he continued.) 



