176 



STUDIES IN FOSSIL BOTANY 



sions ; where the external surface is perfect, it is 

 completely invested by the overlapping laminae of the 

 sporophylls, which are closely packed together (Fig. 70). 

 When the preservation is less complete, the free tips 

 of the laminae have perished, leaving only their more 

 solid basal portions, which often assume a hexagonal 

 form from mutual pressure. The fractures of the casts 



often show something 

 of the internal organ- 

 isation, the tissues being 

 preserved to some ex- 

 tent, though in a car- 

 bonised condition (Fig. 

 70). It is only, how- 

 sm ever, in the petrified 

 sph specimens that the 

 structure is completely 

 revealed 



Yw,. 1 T..—Lepidostrobus. Diagram of heterosporous 



cone in radial section, ax, axis ; s£h, sporo- Our more detailed 



phylls; sm, sporangia, seated singly on the . 



upper surface of each sporophyll ; lg, ligules ; description will be 



the microsporangia, in upper part of cone, con- U J r j 



tain numerous microspores, while the mega- Dase( l on a IOrm named 



sporangia below are shown containing four U,, Wf'lKamc^n T „,A„- 



megaspores each. (G.T.G.) W W1| UamS0n Lepl- 



dostrobus oldhamius} of 

 which several examples in a calcified state have been 

 yielded by the calcareous nodules of the English Coal- 

 measures. 



The largest specimens of this strobilus reach a 

 diameter of about 4 cm. ; the axis is slender, about 

 4 or 5 mm. in thickness. The anatomical structure 

 is of the usual Lepidodendroid type. The centre of 



1 For a full illustrated account of the organisation of these cones, see 

 Maslen, " Structure of Lepidostrofois," Traits. Linn. Soc. vol. v. 1899. 



