SPORE-PRODUCING MEMBERS 



325 



sub-genus Rhopalostachya, while hi the simpler Sctago-forms the sporophylls 

 are as in L. Brownii, or, better still, in Pinakodendro?i. The wall of the 

 mature sporangium is frequently represented by the single prismatic outer 

 layer alone, the inner thin-walled layers seen in Z. Brownii being absent : 

 this difference is comparable to that seen in Lycopodium, where the mature 

 wall usually consists of a single layer, but in L. dichotomum of several 

 layers. There is also some 

 divergence in detail of the 

 internal upgrowths from the 

 basal ridge : in most Lepi- 

 dostrobi these take the form 

 of longitudinally disposed 

 plates, of which one or more 

 project upwards into the 

 sporangial cavity. Lastly, 

 there is the fact of hetero- 



spory, 



which has now been 



established in a number of 

 examples, though it must 

 not be assumed for them all 

 without actual demonstra- 

 tion. Such differences as 

 those mentioned are, how- 

 ever, of secondary impor- 

 tance, and in the general 

 morphological character of 

 the Lepidodendroid cones 

 there is substantial unifor- 

 mity as regards the relation of 

 sporophyll and sporangium, 

 as well as in their form. 



The fructifications of 

 Sigillaria appear as cones 

 sessile, but more 

 borne on long 

 lateral branches, which are 

 covered below with acicular 

 bracts : such strobili are thus more strongly differentiated from the 

 vegetative axes than is the case in Lepidodendron. The plan of construction 

 of the cone itself appears to have been the same, and though its preservation 

 is commonly imperfect, it seems that the sporangia of Sigillaria resembled 

 those of Lepidodendron in their form and mode of insertion, as also in the 

 existence in them of a heterosporous condition. They were sometimes of 

 large dimensions : frequently, however, of smaller size. Among them a 

 small cone, described by Zeiller as Sigillariostrobus Crepini, differs from 



cue 



FIG. 170. 



Lepidostrobus Veltheimianus. Longitudinal section of cone, 

 showing microsporangia above and megasporangia below. ax= 

 axis of cone, snowing stele, /, and leaf-traces, passing out to 

 sporophylls, br', nii= microsporangia ; trta = megasporangia con- 

 taining a few spinose megaspores. X about 4. (From Scott's 

 Studies in Fossil Botany.) 



