360 KIDSTON : THE FLORA OF THE CARBOXIFEROUS PERIOD. 
Lepidodendron, Lepidophloios, and Bothrodendron, though they 
possess the essential characters of the Lycopodiacece, appear to have 
entirely passed away without leaving any descendants. 
Sigillaria, in the manner in which the sporangia are immersed 
in the sporophylls, shows considerable affinity with the existing and 
diminutive Isoetes. In fact, Goldenberg, many years ago, stated his 
belief that Sigillaria was an arborescent form of Isoetes, and sub- 
sequent investigations have added much to strengthen this view. 
SPHENOPHYLLACEiE. 
Sphenophyllum Brongniart. The genus Sphenophyllum holds 
a unique place amongst both fossil and recent plants. 
The various species of Spheno- 
phyllum have slender ribbed stems 
with tumid or swollen nodes ; the ribs 
do not alternate at the nodes, but 
continue in the same line. The inter- 
nodes vary considerably in length 
(Sphenophyllum myriophyllum Crepin, 
Plate LXIIL, fig. 2), and the branches 
are given of! at irregular intervals, one 
branch only being given ofi from a node. 
The leaves in the typical form are 
cuneate, Text Fig. 12, A and B, or 
wedge-shaped, but they vary much, not 
only on different species, but even on 
the different parts of the plant, and this 
variation can be observed even on the 
same specimen. The normal wedge- 
shaped leaf passes into leaves divided 
into two deeply-cut lobes (Sphenophyllum ma jus Bronn. sp., Plate 
LXIL, a at a), which again are bifid, or they may be reduced to 
dichotomously-divided filiform segments which radiate fan-like from 
the base. Text Fig. 12, C, or may even be simple, narrow, lanceolate 
leaves forming a whorl round the stem. These latter seem to be 
restricted to the larger branches. The nervation repeatedly bifurcates, 
a single veinlet going into each tooth or segment of the leaf. 
Fig. 12. — A and B, Spheno- 
phyllum cwiefolium Sternb. 
sp. A, Whorl of leaves, 
natural size (No. 2706). B, 
Leaf, enlarged to show teeth 
and nervation (No. 1566). 
C, Sphenophyllum trichoma- 
tosum Stur, natural size (No. 
1046). 
