FOSSIL VASCULAR CRYPTOGAMS 



125 



like sporangiferous spikes of Equisetum. It contained spores of one 

 kind only. 



The group of Calamarie.e — including the stems known as Cala- 

 mites and CaIamode?idron, and the fruit known as CaIa?nostachys — 

 have been separated by some authorities from the Equisetaceae on the 

 ground of their alleged heterospory, but without sufficient warrant from 

 the facts of their structure as actually observed. 



The remains of Calamites occur in immense quantities in the Car- 

 boniferous strata ; apparently they 

 constituted one of the most im- 

 portant features of the vegetation of 

 that period, disappearing after the 

 Permian. The stems were fre- 

 quently of gigantic dimensions com- 

 pared with our existing Equisetums, 

 attaining a height of thirty feet and 

 a diameter of four inches or more. 

 They consist of a hollow central 

 cavity, with a cylinder of tracheides 

 in wedge-shaped bundles, separated 

 at their origin by parenchyme, and 

 alternating at the nodes, where there 

 is a diaphragm or ' phragma.' The 

 leaves, which spring in whorls from 

 each node, do not, as in Equi- 

 setites, coalesce laterally into sheaths 

 surroundino; the stem. Thev are 

 narrow and acicular, with a single 

 prominent midrib. At the nodes 

 are occasionally seen saucer-shaped 

 depressions, the scars of the lateral 

 branches, which are sometimes 

 found attached to the primary axis. 

 The growth of the stem is characterised by a considerable secondary 

 increase in thickness ; and, since this phenomenon was formerly un- 

 known among living Vascular Cryptogams, it has induced some authori- 

 ties to transfer those examples where it occurs, under the name of 

 Calamodendrese, to Gymnosperms ; but this has been rendered un- 

 necessary from the fact that a secondary growth in thickness occurs 

 also in Lepidodendron and Sigillaria, as well as in Isoetes; and is 

 further contradicted by the fact that fructification of an evidently 

 cr}-ptogamic character has been found in organic connection with stems 



Fig. 96. — A, Phyllotheca eqtdsetiformis ; B, 

 fructification of Phyllotheca. (After Solms- 

 Laubach.) 



