56 SCIENCE PROGRESS. 



regards the central axis of the strobilus, its structure closely 

 corresponds to the stele of Spkenophyllum as described by 

 Renault * and Williamson.' 2 



Zeiller's figures and comparative measurements admit 

 of no doubt as to the identity of B. Dawsoni and Spheno- 

 phyllum c unei 'folium (Sternb.) var. saxifragcefolium. It is 

 now generally admitted that the great variation in the form 

 of Spkenophyllum leaves, from the broad wedge-shaped 

 and multi-nerved, to the narrow and linear-lanceolate, 

 single-nerved form, is simply a proof of the dimorphic 

 character of some examples of the genus. As Zeiller 

 points out, there are still some points to be cleared up with 

 reference to the structure of the Spkenophyllum strobili. 

 In 1876 Renault suggested that Sphenophyllum was he- 

 terosporous. :! Zeiller has examined Renault's silicified 

 specimens, and concludes that they furnish no trustworthy 

 evidence on which to base such a statement. 



After considering examples of those species of Spheno- 

 phyllum of which the strobili are known, Zeiller goes on to 

 discuss the question of botanic affinity. There is a striking 

 similarity between the ovoid sporangia of Sphenophyllum, 

 supported on their slender pedicels, and the sporocarp of 

 Marsilia, especially such a species as M. pubescens Tenore, 

 in which the pedicel is adnate to the sporocarp for about 

 half its length. In Sphenophyllum the pedicel is traversed 

 by a vascular bundle, and arises from the ventral face of a 

 bract, either in its axil or at a greater or less distance from 

 the axis of the strobilus ; in Marsilia the pedicel is a ventral 

 lobe of a leaf, and is detached from the leaf-petiole either at 

 its base or some little distance above it. In Sphenophyllum 

 each pedicel bears one sporangium : in Marsilia each pedicel 

 represents a foliar limb folded in two halves, in each of which 

 are several sporangia. Possibly, then, we may regard the 

 sporangium stalk of Sphenophyllum as homologous with the 

 sporocarp stalk of Marsilia. The external layer of the spo- 



1 Ann. Sci. Nat. Bot. Ser. 5, vol. xviii., 1873, p. 5. 



1 Phil. Trails., 1874, p. 41. 



3 Ann. Sci. Nat. Bot. Set:, vi., p. 303. 



