94 BOTANICAL GAZETTE [august 



basis the conclusion has been formed in certain cases that an increase 

 in number of sporangia by septation has occurred. It is concluded 

 that these late differentiated sterile tracts were once in the race 

 fertile and that they were subsequently diverted from this previous 

 condition; in fact that the ontogenetic development reflects the 

 evolutionary history. This is exemplified in the synangia of 

 Tmesipteris and the sporangia of Isoetes" (Bower 7). 



In the ontogenetic development of the sporangium of Isoetes 

 and Lycopodium and the synangium of Tmesipteris (one of the 2 

 genera of the order Psilotales) there are no structures developed 

 which might, like the sterile tissue within the immature sporangium 

 of Lepidostrohns Oldhamius, suggest reduction in descent from a 

 more intricate or elaborate form. The relation of the Isoetales 

 to the remaining orders of the Lepidophytes is still very obscure, 

 but is certainly closer to the Lepidodendrales than to any other, 

 if we may judge by the radial elongation and insertion of the 

 solitary sporangium; the trabeculae within this organ suggesting 

 the rodlike or peglike processes within the sporangium of Lepido- 

 strohus Brownii; the Hgule; the secretory strands, comparable to 

 parichnos observed in the leaves of one species; the great develop- 

 ment of cortex, analogous to the enormous development of second- 

 ary cortical tissue, chiefly phelloderm, in the tree Lycopods of the 

 Paleozoic; the secondary increase in the stem in which new zones 

 of cells may have periodically taken up the cambial activities; and 

 the dichotomous, monarch roots, like those of Stigmaria. 



We are inclined to believe with Bower, Scott, and Thomas (32) 

 that the furcate sporophyll with a synangium (not much unUke 

 the group of sporangia upon the sporophyll of Sphenophyllum fnajus) 

 resting upon its adaxial surface below the point of bifurcation in 

 the Psilotales and the triarch stele with the xylem elements extend- 

 ing to the center in the smaller branches of Psilotum would seem 

 to indicate that this group is related to the Sphenophyllales perhaps 

 more closely than to any other. The stele in the stem of Psilotum 

 is not much unlike that in the axis of the cone of Cheirostrohiis, one 

 of the Sphenophyllae from the Calciferous sandstone of Pettycur, 

 Firth of Forth; and this, with the formation of secondary xylem 

 at the base of the aerial stem and in adjoining parts of the rhizome 



