404 SPHENOPHYLLALES. A. SPHENOPHYLLEAE 



were united at the base into a narrow sheath or collar surrounding the 

 axis. The transition to the strobilus is plainly seen at the lower limit of 

 the large specimen from the Brussels Museum, described and figured by 

 Kidston : towards the upper limit of the specimen, where the sporangia 

 cease, the axis is continued in the vegetative manner, with longer internodes. 

 These facts plainly point to the absence of a highly differentiated strobilus, 

 and the existence in this species of a " Se/ngo" condition, where the fertile 



region is a mere zone on a continued axis. Not 

 only does S. majus stand as yet alone in the genus 

 by the indefiniteness of its cone, but also in the 

 character of its sporangiophores. One of these is 

 borne near to the base of each forked sporophyll 

 (Fig. 222) : the sporangia, which are 4-6 in 

 number, but usually four, are grouped round a 

 central attachment : and though no elongated 

 pedicel can be seen, still the fact that when they 

 are removed from the bracts they still remain 

 united in groups of four to six indicates that 



they had a common base. In favourable cases 

 sp rans Kidston has been able to demonstrate that a 



radial line of dehiscence is clearly marked, 



corresponding in position to that of the synangium of Psilotiim, to which 

 the whole structure shows a remarkable resemblance. As a last type, and 

 not the least remarkable of this variable genus, may be mentioned the 

 fructification of S. fertile, recently described by Scott. 1 It is characterised 

 by the fact that both the "dorsal and ventral lobes are fertile," by which 

 is meant that the bract bears sporangia as well as the sporangiophore, 

 which it subtends. Dr. Scott remarks that this is " more probably due to 

 special modification than to retention of a primitive condition." \Vith 

 this opinion I readily concur, adding the further comparison of this 

 condition with the common variation of Botrychiitm Luuaria, where the 

 sterile leaf is often partially, or even completely fertile (compare Fig. 85). 

 Lastly, there remains to be described that remarkable cone from the 

 Calciferous Sandstone of Burntisland, named by Scott Chcirostrolnis, and 

 placed by him in relation to the Sphenophyllales, while recognising also 

 its affinities with the Equisetales and Lycopodiales - The vegetative system 

 of the plant of which this is the fructification is still unknown. The cone 

 itself is of large size, and shows greater complexity than any of the known 

 sporangiophoric types. The robust axis shows structural characters sug- 

 gestive of a Lycopodinous rather than of a Sphenophylloid affinity : the 

 central stele in transverse section has a solid star-shaped xylem-core, with 

 twelve projecting protoxylem-groups, corresponding to the series of sporo- 



1 Proc. /vVi'. Soc., Dec., 1904, and Ann. / Ac/., xix., p. 168, also Pro, l\<i 



Bota>n,\ \. p. 151. 



-Scoti, /'////. Trnns., vol. iSon, 1897, "On ( 'hcin .Mrobus. " 



