272 EQUISETALES 
separated by leaf-sheaths (Fig. 196). It is thus seen that the strobilus of 
Lyuisefum is not always that circumscribed terminal body which is typical 
for the living species. 
The Lyuiselum-type has been recognised, though with some uncertainty, 
and only in few specimens, as far back as the Middle Coal Measures ;! 
but it is seen represented more commonly, 
and by large forms, in the Mesozoic rocks. 
Related to it are two other fossil forms: 
the genus Pyllotheca of Permian age 
resembles Zguzse¢um in the general features 
of the shoot, with its cup-like leaf-sheaths 
webbed at the base, but differing in the 
form of the leaves and in the fertile 
region : this is constructed on the general 
plan of £guisetum, but with the strobilus 
interrupted at intervals by sheaths of 
sterile leaves, as in some abnormal con- 
ditions of Lyuitsetum (Fig. 197). Some 
specimens of Phyllotheca have, however, 
been described by M. Zeiller as having 
strobili like those of Aznularia, that is, 
of the Calamostachys-type.2 The other 
genus is Schizoneura, of ‘Triassic age, 
characterised by the whorled leaves being 
associated in webbed sheaths, which may, 
however, be slit longitudinally to the base. 
They thus form leaf-like lobes which stand 
off at a considerable angle from the axis 
(Fig. 198). The axis is marked by longi- 
tudinal grooves, which are continuous 
Fic. 195. longitudinally from internode to internode, 
Equisctun maximum, Link. A, the thus showing that the leaves of successive 
f a fertile a th the | : po ‘¢ 
Beene eae eee ue “peipe Whorls did not alternate. The fructifi- 
leaf-sheath. @=annulus. 2 =stalks of spor- 3 5 v 
angiophores cut off. 3/= transverse section of cation is unknown. 
axis. #=sporangiophores in various posi- Most of the older Equisetal fossils, 
tions, sl gbtly enlarged. sf=stalk. sg= 
sporangia. s Sealaveed distal end. (After however. belong to the Calamarian type. 
Sachs.) ’ 
These plants were often of dendroid habit, 
with secondary thickening of the stem, but with a similar primary 
construction of the shoot to that seen in Lgwisedum. The leaf-whorls 
are frequently webbed at the base, though often only slightly, as in 
Annularta; but in Asterophyllites, which is traced back to the Devonian 
period, the leaves appear quite separate, in widely divergent whorls. 
‘Kidston, **On the occurrence of the genus Aygzdsetam, etc.,” Annals Mag. Nat. 
Hist., ix:, pi 138, 1892. 
*Zeiller, Palaeoholanigue, \. 164. 
