402 STUDIES IN FOSSIL BOTANY 



happens also to have been most completely investigated. 

 The specimens, with structure preserved, were first 

 discovered in 1871, among the calcified remains 

 brought to light in that year by Mr. G. Grieve, at 

 Pettycur, near Burntisland, in Scotland ; the horizon 

 of this bed, which has often been referred to. above, 

 is that of the Calciferous Sandstones. The plant was 

 described by Williamson, who at first named it Dicty- 

 oxylon Grievii, but shortly afterwards (1872) placed it 

 in Corda's genus Heterangium, which up to that time 

 had only been known from a single fragment. 



In the case of Heterangium we have as yet no 

 certain knowledge of the reproductive organs, and the 

 reference of the genus to Lyginodendreae is therefore 

 based entirely on vegetative characters. 



The specimens of Heterangium Grievii are numerous 

 in the Burntisland deposit, and the structure is often 

 very well preserved, as in the specimen represented, in 

 transverse section, in Fig. 155. To quote Williamson's 

 words, it " always appears in the form of straight, 

 slender, unbranched stems." Branching, however, may 

 have occurred occasionally, for we have found one 

 instance in a closely allied species (H. Lomaxii), but 

 in any case it must have been rare. The restoration 

 of a portion of stem, shown partly in section and 

 partly in surface-view, reproduced in Fig. 154, from 

 Williamson's original memoir, 1 gives an accurate idea 

 of the general structure. In external form the stems, 

 which have not been found to exceed about 1.5 cm. 

 in diameter, are angular ; the projecting ribs are 



1 " Organisation of Fossil Plants of Coal-measures," Part iv., Phil. 

 Trans. 1873. 



