LYCOPSIDA 73 



expanded apex of the sporophyll (Fig. 12E). The sporangium 

 wall was only one cell thick at maturity and dehisced along 

 its upper margin. Megaspores and microspores must have 

 been produced in enormous numbers, for they are extremely 

 abundant in all coal-measure deposits. Some megaspores 

 have been found with cellular contents, representing the 

 female prothallus, retained within the megaspore wall 

 ('endosporic') as in Selaginella today, and occasionally 

 archegonia can be recognized. 



The number of megaspores produced within each mega- 

 sporangium- varied considerably from species to species, and 

 in some was restricted to one. In Lepidocarpon (Figs. 12F 

 and 12G) the megaspore was retained in the sporangium, 

 which, in turn, was enveloped by two flanges from the stalk 

 of the sporophyll. The whole structure was shed Hke a seed 

 from the parent plant and has been regarded by some 

 botanists as actually being a stage in the evolution of a 

 seed. It would be much safer, however, to regard Lepido- 

 carpon as merely analogous to a seed, for the sporophyll 

 flanges are quite unlike the integuments of true seeds, except 

 perhaps in function. It is not known whether the micro- 

 spores germinated within the sht-hke 'micropyle' while the 

 megasporophyll was still on the tree, or whether it did so 

 after it had fallen to the ground. 



Sigillaria (Fig. 12H) is characterized by the arrangement 

 of its leaf bases in vertical rows (Fig. 12I). It branched 

 much less than Lepidodendron or Lepidophloios and it bore 

 its cones in a cauliflorous manner. Furthermore, the leaves 

 were much longer, up to i m, grass-Hke and, in some species, 

 had two veins, possibly formed by the forking of a single 

 leaf-trace. Species from the Upper Carboniferous were 

 similar to Lepidodendron and Lepidophloios in their internal 

 anatomy, having a medullated protostele with a continuous 

 zone of primary wood. Some of the Permian species, e.g. S. 

 Brardi, however, showed a further reduction of the primary 

 wood, which was in the form of separate circummedullary 



