iqiq] BASSLER—SPORANGIOPHORIC LEPIDOPHYTE 93 



have become almost axiomatic and may be accepted here without 

 argument. The regular recurrence of red beds and sometimes salt 

 and gypsum-bearing deposits toward the close of each great period 

 conveniently marks these subperiods of continental expansion. 

 In the Appalachian province where the Paleozoic record is unusually 

 complete, we find the Juniata and Red Medina at or near the 

 top of the Ordovician. the Salina toward the top of the Silurian, 

 the Hampshire and Catskill occupying the same position in the 

 Devonian, the Mauch Chunk in the Mississippian, and many red 

 beds in the Permo-Pennsylvanian, the lowermost already occurring 

 well toward the base of the Conemaugh. That periods of relative 

 aridity and reduced temperature are in general unfavorable to 

 plant life scarcely admits of argument, and thus during the descent 

 of the cryptogams there have repeatedly been periods of stress 

 during which some of them, accustomed to a certain habitat, were 

 in all probability forced to adopt some program of reduction of the 

 sporophyte in order to maintain themselves there. Allied forms, 

 on the other hand, might be expected to occupy certain sheltered 

 coastal regions where in spite of cold or general climatic aridity 

 they could maintain themselves with little or no reductive changes, 

 and thus it would come about upon the return of generally favorable 

 conditions that the reduced and the primitive types might occur 

 together. Arboreal types by reason of the specialization incident 

 to this habit were doubtless upon the whole more sensitive to 

 changes in the environment than the lowly herbaceous or sutfrutes- 

 cent forms, and it would seem very difficult to account for the 

 absence of evidence of reduction among dendritic types that had 

 survived the unfavorable periods toward the close of the Silurian, 

 the Devonian, and the Mississippian. 



Whether or not the Psilotales, the Isoetales, and the Lyco- 

 podiales (the last named, it must be remembered, are restricted 

 in this paper to the Lycopodiaceae and the Selaginellaceae) belong 

 to the phyletic line here proposed for the Cantheliophorales and 

 the Lepidodendrales, is the question that now suggests itself. 

 "When in a tissue tract the distinction between vegetative and 

 sporogenous cells takes place late in the individual the presumption 

 is that the distinction has been of late origin in the race. On this 



