SPORE-PRODUCING MEMBERS 



323 



shows a structure similar to thatsof Lepidodendron Harcourtii^ and though 

 there is no direct indication of the source of the cone, comparison of the 

 structure with that of Lepidodendron stems, and with other Lepidodendroid 

 cones, leaves no doubt of its being the strobilus of a Lepidodendron. The 

 axis bears numerous sporophylls, of which thirteen are usually represented 

 in each transverse section : the basal region of each extends horizontally 

 from the axis, and supports the sporangium, which may extend for fully 

 half an inch along its surface (Fig. 168). The distal end of the sporo- 

 phyll turns upwards, without any peltate expansion. 



FIG. 169. 



Lepidostrobus Brotvnii. A= wall of sporangium, showing outer sclerotic cells (scl), 

 with several thin-walled layers within. X 100. B = three sporangia in transverse section 

 of the cone ; r= median ridge. X 3. C = cone in tangential section. D = sporangium in 

 tangential section of cone, slightly diagrammatic; .$/ = sporophyll ; r=sub-archesporial 

 ridge ; v, b = vascular bundle ; / = processes rising from the ridge. X6. E= small part of 

 the base of a sporangium in radial section, showing the processes /$, /, which rise from it. 



X20. 



Comparison of transverse and tangential sections of the cone (Fig. 

 169 B, c) gives a clear idea of the form of the very large sporangium, 

 which is a radially extended body, broader and deeper at the distal end 

 than at the proximal ; it is attached throughout its length by a relatively 

 narrow median, flange-like insertion to the upper surface of the sporophyll, 

 and immediately above the course of its vascular bundle. Comparison of 

 its outline with that of the sporangium of Isoetes shows a very striking 

 similarity ; but this is not limited to the form only : in L. Brownii above 



1 Or to that of L. Williavisoni, according to Solms Laubach, Fossil Botany, Engl. 

 ed., p. 226. 



