SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 775 



7. Some of the projections at various levels on the stem gave rise to adven- 

 titious lateral branches. 



8. Some of the lateral branches, attached by a narrow base, were readily 

 detachable and probably served for vegetative propagation. 



9. Dichotomous branching of the stem occurred sparingly. 



10- In the rhizomes and stems, epidermis, outer cortex, inner cortex, and stele 

 can be distinguished. 



11. The epidermis in the aerial stems had a thick outer wall and stomata were 

 sparingly present. 



12. The cortex consisted of a narrow outer zone, which in the aerial stems had 

 the character of a hypoderma, and a broader inner cortex. The more delicate tissue 

 of the inner cortex had intercellular spaces and was in relation with the stomata. It 

 possibly represented the assimilating tissue. 



13. The vascular system consisted throughout of a simple cylindrical stele 

 composed of a slender solid strand of tracheides with broad annular thickenings 

 and no distinction of protoxylem and metaxylem. Surrounding the xylem was a 

 zone of phloem consisting of elongated thin-walled elements. 



14. No vascular strands were given off to the small projections on the stem. 



15. No vascular connection existed between the stele of a lateral branch and the 

 stele of the parent axis. 



16. In the dichotomous branching of the stem the stele divided to supply the 

 two branches. 



17. The plant bore large cylindrical sporangia. The sporangium had a thick 

 wall, and terminated a stout stalk which corresponded to a small stem. 



18. The sporangium contained numerous spores which were all of one kind. 



Concluding Remarks. 



The plant which has been described (whatever the precise age of the Old Red 

 Sandstone Beds in which it is found may prove to be) is the most ancient land plant 

 of which the structure is at all fully known. By a fortunate circumstance of its 

 preservation in large quantity as it grew, its external form, structure, and sporangia 

 are known almost as well as if we were dealing with an existing species. 



It will be evident that the simplicity of the general organisation and of the 

 anatomy of Rhynia has important bearings on the origin of the sporophyte and its 

 differentiation into stem, root, and leaf in the Pteridophyta. While fully alive to 

 the interest of this, we do not propose in the present paper to consider the bearing 

 of the new facts here brought forward on these speculative questions. We hope to 

 consider them later. 



In attempting to indicate the position of Rhynia Givynne-Vaughani in the 

 vegetable kingdom, it will be sufficient to briefly compare it on the one hand with 



