558 THE AMERICAN MIDLAND NATURALIST 



L. glabrum, however, this tissue is so much more developed that the character 

 has probably become hereditary. Concordantly the seed megaspore of L. 

 glabrum also occupies proportionally less space in the sporangium than in 

 those of other lepidocarps. This appears to be true, at least in so far as the 

 sections shown on Darrah's Plate II are typical of the species. In the lomaxi 

 group and in Illiniocarpon there is no comparable development of the "nutri- 

 tive" tissue. 



Darrah's species therefore probably lacks diagnostic features which assured- 

 ly would place it in the genus Lepidocarpon and in addition shows other modi- 

 fications which indicate considerable divergence from that group. Because of 

 the lack of a prismatic palisade layer, Fredda Reed's specimens may occupy an 

 intermediate position between Lepidocarpon Scott and Darrah's divergent 

 type, L. glabrum. It is important that the divergent characters of the latter 

 be recognized, and the writer regards them, in conjunction with the lack of 

 information in other particulars, as conclusively indicating a need for L. 

 glabrum, at least, being classified under a distinct generic name. However, 

 there is no basis for doubting that its relationship is definitely with the Lepido- 

 carpaceae. 



Darrah's comparison of Lepidocarpon glabrum with Lepidocystis is highly 

 significant, and it may be that this ambiguous and poorly defined group will 

 be clad with useful biological meaning after all. The Lepidocarpon described 

 by Reed from Harrisburg coal balls, which also lacks a prismatic sporangial 

 wall, is not integumented and may not be abnormal as Reed supposed. It also 

 might be classified with this divergent lepidocarp group having "lepidocystoid" 

 characters. However, there appears to be considerable disharmony among speci- 

 mens which have been labeled "Lepidocystis" in the past. Few of them have 

 been shown to possess spores in place, but those specimens in which spores have 

 been recognized are clearly referable to the free-sporing lycopods, probably to 

 the Lepidodendraceae. It is altogether possible (in fact, probable, in view of 

 L. glabrum) that many specimens which do not appear to have spores, actually 

 enclose unrecognized seed megaspores of the cystosporean type. These speci- 

 mens would necessarily belong in the Lepidocarpaceae. The availability of the 

 name Lepidocystis for lepidocarp species with this latter character evidently 

 must be determined by restudy of the genotype which is Lepidocystis pectinatus 

 Lesquereux. 7 



The conclusion that there are at least two divergent branches of the primi- 

 tive integumented lepidocarp stock in the American Pennsylvanian is plausible. 

 One branch shows greater specialization of the integuments and other struc- 

 tures and is represented by Illiniocarpon. The other branch is represented by 

 L. glabrum in which the seeds have been subject to a different kind of speciali- 

 zation involving, probably, loss of the integument. Presumably the less special- 

 ized true Lepidocarpon type coexisted with both of the more specialized line- 

 ages, but the ancestry of the latter groups may be sought among the more 

 primitive lepidocarps that geologically antedate them. 



7 The holotype of this species is listed in Lesquereux' "Coal Flora" as No. 423 

 of the Lacoe collection, now in the U. S. National Museum at Washington, D.C. 



