1 76 EQUISETACEAE, MARSILIOIDEAE, 



that of the Trias, the most gigantic forms of the group being peculiar to the 

 upper members of that formation. Their importance in the general vegeta- 

 tion diminishes as we reach Jurassic times, while in the Coal-measures in 

 the other direction only a few impressions have been found and these not 

 wholly above suspicion. 



The best-known remains of Equiseteae belong to the genus Equisetites, 

 which Schimper frankly terms Equisetum. One of the most typical species 

 and at the same time the most gigantic in size is Equisetites arenaceus, 

 Bronn, which is characteristic of the Keuper and especially of the Letten 

 Kohle, and is found in splendid specimens in the Stuttgart Schilfsandstein 

 in the neighbourhood of Wiirzburg and Heidelberg. Many good figures of 

 it are given in Schimper l . This species has been found in the above loca- 

 lities in very various states of preservation Large cylindrical pieces of erect 

 shoots which may be of the thickness of an arm are of very frequent occur- 

 rence, and show the leaf-sheaths and the surface of the internodes both in the 

 mould and on the cast. The surface is characterised, as in living species, by 

 alternating ridges and furrows, which are not very prominent on the whole 

 but become more distinctly marked towards the sheath. The alternation of 

 these is often plainly to be seen on the successive internodes, but is some- 

 times obscure. The sheaths are tubular and are closely applied to the stem ; 

 they have their upper margin divided into short but very numerous teeth 

 (Schimper states that he has counted more than one hundred in stout speci- 

 mens), and each tooth ends in a long thorn-like process. The basal portions of 

 the erect shoots, by which they are attached to the rhizome, are sometimes 

 disclosed to view. Pieces of stem of this kind narrow gradually and become 

 conical, the internodes being shortened at the same time ; they are thus 

 easily distinguished from the upper extremities of shoots, which are also 

 sometimes preserved and are seen to narrow but slightly and to be 

 rounded off into a dome-like termination. We sometimes get a view of 

 such shoot-tops, especially in buds formed on the rhizome, either vertically 

 compressed or from above 2 , and then the shortened internodes with their 

 sheaths are seen as so many concentric circles. 



Nodal diaphragms of solid construction are found in Equisetites 

 arenaceus, as in our living species ; they are often preserved, and are then 

 usually attached to the sheaths which belong to them. They are not 

 unfrequently disclosed in splitting the stone, especially where the stems lie 

 across the stratification ; the sheath is in that case always vertically com- 

 pressed and spread out flat. The diaphragm, when well preserved, shows a 

 flat unsculpturcd central field and a raised and rounded ring, in which the 

 impressions of the vascular bundle-system can be distinguished as radiating 

 furrows or folds. It is possible that Emmons' 3 genus Lepacyclotes from the 



Schimper (1), tt. 9-11. a Schimper (1), t. 9, f. 3. s Emmons (1), t. 3, ff. 4, 6. 



