1920] on The Earliest Known Land Flora 141 



But near to their base there are "hemispherical projections.'" appa- 

 rently of superficial origin. Some of these gave origin to tufts of 

 hair, but others produced adventitious branches, which having 

 narrow bases were easily detached, and served as means of vegeta- 

 tive propagation. Though these organs are not easily ranked with 

 those of living plants, they are something in advance of what is 

 seen in Uornea and B. major. The sporangia are relatively small, 

 and there is no clear evidence of their dehiscence. 



The largest, as it is also the most complex, of these plants is 

 Ash roxylon Mackisi. Its base consisted of branched rhizomes, which 

 burrowed after the manner of Stigmarian rootlets, and each was 

 traversed by a vascular strand with undifferentiated xylem ; but 

 curiously enough rhizoids are absent. These rhizomes passed over 

 into upright aerial stems, which attained a diameter of as much as a 

 centimetre, and had a complex structure (Fig. 5). They forked, and 

 bore externally small and simple leaves. The stele had a stellate 

 xylem very like some Lycopods. From its rays issued strands passing 

 to the bases of the leaves, but not entering them. As in Lycopodium, 

 more than one vertical series of leaf-traces may issue from each ray 

 of the stellate xylem, a fact that confirms the Lycopod comparison. 

 Longitudinal sections show the relations of epidermis, cortex, phloem 

 and xylem, and the way in which the inner cortex of stem and 

 rhizome often contain fungal hyphae. It is possible that in the 

 rhizome these may have been concerned in mycorhizic nutrition. 

 Higher powers demonstrate the tracheides as irregularly, or spirally 

 barred, but not scalariform. An endodermis has been seen delimiting 

 the cylindrical stele, and mesarch protoxylem is found in the xylem- 

 rays. The leaves are parenchymatous, the vascular strands stopping- 

 short at their bases. The epidermis has been found to bear very 

 perfect stomata. The essential points of structure of the plant are 

 thus fully known. 



In certain blocks sporangia have been found attached to pro- 

 fusely dichotomising stalks of simpler structure than the main steins 

 of Asteroxylon, and not definitely attached to them. They are asso- 

 ciated, however, with stems of Asteroxijlon, while those of Eornea 

 and Rhynia, from which they are structurally distinct, are absent 

 from the blocks. The association makes it probable 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 Asteroxijlon was thus more 

 advanced in various respects than any of the other three plants of 

 the chert. 



Comparison of these four fossil species from Rhynie with other 

 fossils already known from the Lower Devonian Period shows that a 

 very homogeneous flora existed at that time, consisting chiefly of 

 leafless and rootless land-living plants. These and other characters, 

 such as their large, distal, sometimes solitary, and often forked 



