SPHENOPIIYLLEAE. 



273 



phragms at the nodes as in the Equisetaceae ; the internodes, which were from five to 

 six centimetres in length, were hollow. The leaves were a characteristic feature of 

 the group, not being united into a sheath as in the Equisetaceae, but disposed separately 

 in whorls at the nodes, lanceolate and with a mid-rib. The structure of the stem, so far 

 as it can be determined, was the same as in Equisetum. The branches were in two 

 rows on the stem ; only the two opposite leaves in each whorl bore each a shoot in 

 its axil. 



The sporangiferous spikes, known a.sBri{ck//ianma,7in(\ assigned to /^;/;?//'Air/<^7, differed 

 considerably from those of existing Equisetaceae, and especially in the circumstance that 

 sterile leaves alternated in them with fertile (sporophylls) '. The sporophylls bore four 

 sporangia ; in the lower part of the spikes the sporangia contained macrospores which 

 were twelve to fifteen times larger than the microspores found in the upper sporangia. 



2. Similar sporangiferous spikes appear in the group of the Equisetineae known as 

 AsTEROPHYLLlTES, but our knowledge of them is very defective, especially in all points 

 connected with the spores. These plants had jointed stems and branches, and at the 

 nodes whorls of linear erect leaves with a mid-rib. The branches also were in whorls. 

 The sporangiophores, in form like the sporophylls of the Equisetaceae and agreeing 

 with those of the Annularieae, were placed between and a little above the sterile leaves 

 (bracts) of the spikes, while the sporangiophores of Annularia were inserted at about the 

 middle of the internode between two sterile whorls. The number of the sporangiophores 

 also was only about half the number of the sterile leaves, but the sporangiophores do 

 not appear to have been axillary but to have been placed between two sterile leaves, 

 and were most probably here as elsewhere only modified leaves. 



III. SPHENOPHYLLEAE \ 



This interesting group of fossil species is not closely allied to any existing forms, 

 and has consequently been associated with very different families. They are herbaceous 

 plants, with simple or branched, and furrowed stems ; but the furrows do not as in the 

 Equisetaceae alternate with one another on successive internodes. Sessile cuneiform 

 leaves without a mid-rib, but traversed by bifurcating veins of uniform size, are 

 inserted in whorls on greatly enlarged nodes. The sporangiferous spikes are cylindrical, 

 the bracts and sporangia in whorls. The Sphenophylleae have Httle in common with 

 the Annularieae and Asterophyllites except the verticillate arrangement of their leaves, 

 and they differ from them especially in the structure of the stem. The diameter of 

 the stem is from one and a half to fifteen millimetres ; in the centre of the stem is a three- 

 cornered mass of tracheides or vessels, in which pitted, scalariform and spiral elements 

 succeed one another from within outwards. The leaf-traces, which in Sphenophyllum 

 quadrifidiim consist of two bundles, connect with the corners of the central mass at the 

 nodes, and each bundle bifurcates in the cortex ; (Renault conceives that the central 

 mass is composed of three vascular bundles, each with two groups of tracheae lying 

 at the comers, the central tracheides being formed subsequently, as they are in the 

 roots). The central mass is surrounded by a tissue of peculiar structure, which we 

 must not describe here. Macrosporangia and microsporangia are together on the 

 same spike ; the sporangia are placed upon the base of the leaves, as in Lycopodium, 

 the macrosporangia apparently nearer the axil of the leaf than the microsporangia, or 

 in the axil itself. 



1 The relative position of the sterile to the fertile leaves appears to me not sufficiently ascer- 

 tained to admit of further discussion here. It may be remarked that the number of sterile leaves in 

 a whorl is double the number of the fertile in the succeeding whorl. See also p. 195, note. 



2 Renault, Botanique fossile, II. 1882. 

 [2] 



