EQUISETACEM. 



377 



was scarcely more than a thin ring of longitudinal canals, each of which had a few vessels at its 

 outer border In this state the structure of the plant presented a close resemblance to that of a 

 recent Equisetum. But as the plant grew in size, new vessels were added to the exterior of the pre- 

 existing bundles, so that each of the latter became the starting-point of a woody wedge which con- 

 tinued to grow peripherally until it assumed large dimensions. In some specimens these wedges 

 measure fully two inches between the canal marking their medullary angle and their peripheral or 

 cortical base. Each wedge is composed of vertical radiating laminae of barred or reticulated vessels 

 separated by cellular rays. The medullary portion became fistular, as in the recent Equisetaccee 

 at an early age, and the fistular cavities becoming filled with sand or mud, the very thin layer of 

 medullary cells which remained did not prevent the sand from moulding itself against the inner 

 angles of the vertical woody wedges, and thus produced the longitudinal grooves so characteristic of 

 the casts commonly seen in collections. In such specimens most of the vegetable elements dis- 

 appeared during fossilisation, and what remained in the shape of a thin film of coal moulded itself 

 upon the medullary cast, and gave to the specimens the appearance of having had corresponding 

 grooves upon their outer bark surfaces. No single example of a specimen of which the internal 

 organisation is preserved — and we now possess these in great numbers— sustains this conclusion. 

 Wherever the true bark is preserved it exhibits an outline indicating a smooth surface. 



The longitudinal woody wedges of each internode alternated their arrangement at each node ; 

 the wedges of one internode becoming vertically superposed on the larger cellular masses separating 

 the wedges in the nodes above and below. At each node an irregular verticil of vascular bundles 

 left the vascular zone to supply some peripheral organs, probably branchlets ; but besides these 

 diverticula, in one large group an exceedingly regular verticil of canals, with circular or oblong 

 sections, proceeded from the central fistular cavity through the woody zone to the bark. One of 

 these canals occupied the uppermost end of each of the large cellular rays which separated the 

 vascular wedges of each internode. In the common fossils these canals are indicated by a very 

 regular verticil of small round or oblong impressions, which some writers have erroneously asso- 

 ciated with roots, and others with vascular bundles going to leaves or branches. But they never 

 contained any vascular tissues whatever. Of the leaves of Calamites we have no knowledge, 

 although some have identified them with those of Asterophyllites and Sphenophyllum. 



Professor Williamson has only obtained one example of a fruit which he can with confidence 

 identify with Calamites {Volhnannia Daxvsoni, Williamson, in Mem. Lit. Phil. Soc. Manch. 3rdser. V. 

 p. 28). It is a strobilus the structure of the axis of which corresponded most closely with that of 

 a young Calamitean shoot. At each node it has a curiously perforated disk fringed with numerous 

 peripheral bracts. From each disk there projects vertically upwards a ring of slender sporangio- 

 phores, around each of which were clustered three or four sporangia full of spores. These sporangia 

 are so compactly compressed that a transverse section of this fruit presents the appearance of a 

 compact mass of spores, amongst which the outlines of the sporangia are traceable with difficulty. 

 Whilst he has failed to find any tnie stem in which the surface of the bark was fluted, that of the 

 intemodes of this fruit was undoubtedly so. He has not obtained more than half-a-dozen examples 

 of Calamite-stems in which the outer bark is preserved. Nearly all the specimens are absolutely 

 decorticated. Hence we cannot speak with certainty as to what may have been the condition of 

 the surface of the bark in many of these plants. The flutings of the fruit-bark do not, like those 

 seen in the carbonaceous film covering the common casts, correspond in number and position 

 with those caused by the woody wedges, since two vascular bundles are located in each projecting 

 ridge of the axis of the former structure, instead of one as in the latter. 



Mr. Carruthers believes the fruits figured by Mr. Binney, Professor Schimper, and himself, 

 under the several names of Calaiiiodendron commune, Calamostachys Binneyana, and Volhnannia 

 Binneyi (Joum. of Bot. 1867, pp. 349-356), to belong to Calamites; and he further regards the 

 spores as having been furnished with elaters similar to those of Equisetum. Professor Williamson is 

 unable to agree with either of these conclusions. He considers the supposed elaters to be merely 

 fragments of the torn mother-cells of the spores, and that the affinities of these fruits are with the 

 Lycopodiacere rather than with the Equisetacece. — Ed,] 



