(iKXKRAL MORPHOLOGY 



399 



The vegetative system of Sphtnophyllum consisted of a slender axis 

 (Fig. 215), with elongated and fluted internodes intervening between 

 successive superposed whorls of leaves, which in the cone, and sometimes 

 in the vegetative region, were more or less webbed below. The branching 

 of the shoot was irregular and monopodial : the branches were isolated 

 and apparently axillary, 1 though it seems uncertain whether they were 

 not actually, as in Equisetum^ inserted 

 between two of the whorled leaves rather 

 than in the axil of one. 



The leaves in each whorl numbered, 

 as a rule, some multiple of three, six being 

 a frequent number, though as many as 

 twelve, or even eighteen, may be found 

 in some species. They were commonly 

 wedge-shaped, and more or less forked 

 in the venation, with very various cutting 

 extending more or less deeply between 

 the forks. In some of them, and especi- 

 ally in the early forms, the leaves were 

 divided into linear or even filamentous 

 segments (Fig. 216, A, B.). Potonie points 

 out 2 that the earliest forms had narrowly 

 linear, branched leaves, those of later 

 occurrence had larger, more broadly wedge- 

 shaped, and unbranched leaves : thus the 

 size of the leaf increased in the rising 

 geological scale, while the branching of it 

 fell off. But, on the other hand, a striking 

 feature illustrated in the well-known S. cunei- 

 folium was the heterophyllous character. 

 Here on the same plant finely cut leaves 

 may be found below and broader, wedge- 

 shaped leaves above, while in the strobilus 

 the leaves are again finely cut (compare 

 Fig. 215). Commonly the members of one 

 whorl were equally developed, but in the 

 forms from the Glossopteris Flora, named 

 Trizygia, they were unequal. Examples of the leafage of different types of 

 Sphenophylls are shown in Fig. 216, A, B, c, D. The plants were fixed in 

 the soil by diarch roots, which appear to have been borne on the nodes ; 

 but the details regarding them are imperfectly known." The whole plant 

 seems to have been of a weak, straggling character. 



The internal structure possessed greater distinctiveness than the external 

 form, and showed a marked secondary thickening : this originated very 

 1 Scott, Studies, p. 82. - Engler and Prantl, i., 4, p. 516. a Scott, Studies, p. 92. 



Fu;. 215. 



Sphenophyllitm s/>., branched stem, bearing 

 linear and cuneate whorled leaves on different 

 parts. The branch (a) terminates in a long 

 and slender cone. Half natural size. (After 

 Stur, from Scott's Stjidies in Fossil Botany.) 



