CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 



121 



The normal form of leaf is wedge-shaped entire-dentate (fig. 

 21a), bifid or dichotomously divided into narrow segments. In 

 Sphenophyllum trichomatosum (fig. 21c) and Sphenophylluvi 

 tenerrimum the segments are filamentous. A single vein enters 

 the base of the leaf, which by dichotomous division sends off a 

 veinlet to each tooth of the leaf or to 

 each of the segments (fig. 21b). On 

 the majority of the species the leaves 

 are heterophyllous, the entire and 

 much divided forms occurring even 

 on the same branch. This is well 

 shown on a specimen of Spheno- 

 phijllum Schlotheimii figured by 

 Germar.^ 



In Spthenophijllum cuneifolium, the 

 vai: saxifragcefolium, with the much 

 divided form of leaf, is almost invari- 

 ably associated with the cone-bearing 

 branches, though it also occurs on 

 what are apparently barren branches. 

 Probably in all the species, with 

 perhaps the exception of Spheno- 

 phyllum, tenerrimum and Sjtheno- 

 phyllum trichomatosum — which seem 

 constantly to have filamentous seg- 

 mented leaves — a heterophyllous condition of the leaf occurs. 

 This heterophyllous condition gave rise to the opinion that 

 Sphenophyllum was an aquatic plant, the submersed leaves being 

 the much divided ones, the more or less entire leaves forming 

 the aerial foliage. When, however, it is seen that the divided 

 leaves are usually on the stems bearing the fructification, and 

 as undoubtedly the cones were aerial, the presence of these 

 divided leaves gives no support to the view that Sphenophyllum 

 was aquatic ; and further, both forms of leaves occur on 

 the same branch, as on the specimen given by Germar." The 

 internal structure of the stem is also opposed to Sp)henophyUum 

 having been aquatic. 



Fig. 21.— A and B, Spheno- 

 phyllum cuneifoliuin, Sternb. 

 sp. A, Whorl of leaves, 

 natural size {No. 2706). B, 

 Leaf, enlarged to show 

 teeth and nervation (No. 

 1566). C, Sphenophyllum 

 trichomatosum, Stnr, natural 

 size (No. 1046). 



^ Vera. d. Stenik. v. Wettin u. Lobejun, PI. VI. , 

 •3 Germar, I.e., PI. VI., fig. 3. 

 I 



fig. 3. 



