l8o EQUISETACEAE, MARS f LEO IDE AE. 



Heer 1 and Schmalhausen 2 ; in the latter author will be found an incident- 

 ally inserted monograph of the genus. Lastly, Equisetum laterale, Phill. 

 from the Lower Oolite of Scarborough 3 has been removed by Heer to the 

 genus Phyllotheca, to which it must belong rather than to Schizoneura 

 where it is placed by Schimper 4 . 



It is chiefly by their habit that the leafy shoots of Phyllotheca are 

 distinguished from those of Equisetitae. The striation according to Schmal- 

 hausen does not alternate in the successive internodes. The leaf-sheaths 

 are closely appressed, becoming wider and funnel-shaped above in some 

 species ; their margin bears an unusually large number of linear much 

 elongated obtuse one-nerved teeth, which diverge and curve outwards, and 

 are sometimes again incurved at the points and become hooked. These 

 long-spreading sheath-teeth give a very peculiar habit to the genus (Fig. 

 17, A). In Phyllotheca indica and in the Siberian form Ph. deliquescens, 

 Schmalh. the branches are said to be arranged in whorls at the nodes, in 

 other species to stand singly and with their points of insertion in some cases 

 beneath the node-line, in others above it. This is all that I can say with 

 respect to the characters of the branching, as I have no knowledge of the 

 original specimens. Casts accompany some of the species, according to 

 M c Coy and Schmalhausen, and show the well-known striation, but have 

 the nodal lines less deeply incised. If there are any branch-scars, they are 

 placed exactly on the node. 



Circular disks of peculiar appearance are often found with the branches 

 of Phyllotheca, and are usually explained to be the nodal diaphragms of 

 that genus. They lie most frequently on the internodes of the leafy stems 

 on one side of them. They occur with Equisetum laterale, Phill. from 

 Scarborough in the same manner as with the Asiatic forms, and have given 

 it its name, and it is for this reason that Heer has removed the plant to 

 Phyllotheca. The disks show very pretty sculpturing. They are plane 

 and smooth in the middle, but their curved margin is marked with a 

 strong radial striation. I have seen many specimens in the Museum at 

 Oxford with a thick covering of coal, which was split at the periphery into 

 numerous lobes corresponding to the striation, and on the lobes appeared 

 small and peculiar scars. In presence of these facts the usual explanation 

 of these structures appears to me, as to Heer, very doubtful. If it is correct, 

 it is not easy to see why they are so often found in a lateral position at the 

 middle of the internodes ; we are driven to the very arbitrary assumption, 

 that they represent the lowest nodes of the lateral branches which were 

 inserted above the line of the nodes of the stem. 



Various objects have been taken for fructifications of Phyllotheca. 



1 Heer (5), vol. 4 II, t. 4, and vol. 6 I, t. I. '-' Schmalhausen (1), p. 62. 3 Lindley and 



Hntton (1), vol. iii, t. 186. * Schimper (1). 



