154 I>- H. Scott. 



The cones were of large size, attaining a diameter of about 4 cm 

 and a considerable length. The stout axis bears numerous superposed 

 verticils of highly compound sporophylls, the number in each verticil 

 reaching 11 or 12 (Fig. 4). Each sporoph5"ll consists of 6 segments, 

 of which three are dorsal and three ventral; the former are sterile, 

 bract-like organs, while the latter are the peltate sporangiophores, 

 each of which bears 4 sporangia. The great length of the segments, 

 with their slender stalks, and the corresponding elongation of the 

 sporangia, give the cone a peculiar character, but the homology of 

 the parts of the sporophyll with the dorsal and ventral appendages of 

 the Sphenoinhyllmn type of cone is manifest. 



In the sporangia very numerous spores are contained, which, so 

 far as the available specimens show, were all of one kind. 



The axis of the cone is traversed by a polyarch stele, without 

 a pith, but containing scattered xylem-parenchyma among the trachei- 

 des. Secondary vascular tissue was formed in the peduncle, and oc- 

 casionally in the axis of the cone. The prominent angles of the pri- 

 mary wood are equal in number to the sporophjdls in a verticil; at 

 the node a single bundle passes out from each angle, and divides in 

 the cortex into 6 branches, 3 dorsal and 3 ventral, supplying respec- 

 tively the sterile segments and the sporangiophores. The bundle of 

 the sterile segment bifurcates on entering the bifid lamina, Avhile that 

 of the sporangiophore divides into 4 branches, corresponding to the 

 4 sporangia whicli are seated on the thick, peltate head. 



The cone of Cheirostrohus is thus of great complexitj^, and is in 

 fact the most elaborate Pteridophytic fructification known to us. The 

 characters indicating affinity with Sphenophyllum are the following: — 

 the superposed verticils; the dorsiventral lobing and palmatifid sub- 

 division of the sporophylls; the stelar structure (which may be de- 

 scribed as that of a polyarch Splwnophylhim) and the course of the 

 vascular bundles, and lastly the structure of the sporangiophores and 

 sporangia; as regards the points last mentioned a comparison with 

 jBowmanites Dausoni und SpJwnophylhnn fertile is especially indicated. 

 On all these grounds it seems clear that Cheirostrohus finds its natural 

 place in the class Sphenophyllales, as the type of a special famil}'. 

 the Cheirostrobeae. 



The Sphenophj'llales present, as we shall see, evident marks of 

 affinity with the Equisetales, both in their external morphology and 

 in the structure of the sporangiophores and sporangia, as shown most 

 evidently in the case of Cheirostrohus; the connection is sufficiently 

 close to justify Lignier's proposed association of the two classes in 

 a common group, Articulatae. On the other hand the simple, protostelic 

 anatomy is much more primitive than anything we find in Equise- 

 tales, and is rather suggestive of a relationship to Lycopodiales, or 



