CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 



45 



Extending both above and below the leaf-scar is a central keel, 

 which often bears transverse notches on its lower part. Above 

 the leaf-scar and in the line of the central keel is a small 

 cicatricule (c), which has been named by Stur the ligule scar. 

 This little cicatricule is immediately above the leaf-scar in 

 Lepidodendron aculeatum, Sternb., fig. 4c. In Lepidodendron 

 rimosum, Sternb., it is placed a short 

 distance above the leaf -scar (fig. 5). 

 Above the ligule-scar is a transverse 

 triangular notch (fig. 4e), which has been 

 regarded as the homologue of the 1q 



"sporangium attachment" by Stur. 1 



The area surrounding the leaf-scar is 

 called the field (d). In most species of 

 Lepidodendron immediately underneath 

 the leaf -scar are two oval pits (/), one 

 on each side of the keel. These also 

 appear to be glandular or secreting 

 organs. 2 Some Lepidodendra, such as 

 Lepidodendron dichotomum, Zeiller (not 

 Sternb. 1), do not possess them. 3 



On many specimens the so-called ligule-scar cannot be observed, 

 but as it is very small, only well-preserved examples can be 

 expected to show it. In a less degree the same remark applies 

 to the " sporangium notch." I am inclined to think, however, 

 that sometimes these are absent from some individuals — an 

 absence which cannot be ascribed to an imperfect preservation of 

 the fossil. Specimens in my collection support this view. 



If we regard the so-called "ligule-scar" of Lepidodendron as 

 homologous with the ligule-scar occurring in Selaginella — and 

 this interpretation finds support in the investigations of Mr. 

 Maslen, 4 who describes the occurrence of a ligule on the 

 sporophyll of Lepidostrobus immediately in front of the sporan- 



Fig. 5. — Lepidodendron 

 rimosum, Sternb. Leaf 

 cushion, natural size 

 (No. 2438). 



1 Stur, Culm Flora, p. 228, and Explan. to PI. XIX., fig. 1. 



2 Transpiration openings of Potonie, Lchrb. d. Pflanzenpalceontologie, 

 p. 220. 1899. 



3 Zeiller, Flore, foss. Bassin Houil. d. Valenciennes, PI. LXVIL, fig. 1. 



4 Annals of Botany, Vol. XII., No. XLVL, 1898, p. 257. This> referred 

 to more fully under Lepidostrobus. 



