1 9 1 5 } PETRY—OPHIOGLOSSACEAE 357 



in quantity at this location; hence this tissue is not an intrusion of 

 the cortex, but is stelar in character. It is to be noted that this 

 tissue is opposite a break in the endodermis, but not outside it. 



The view is held that there is a morphological distinction 

 between stelar and cortical tissues; that the suberization of the 

 radial walls of a layer of cells is a physiological phenomenon which 

 under the usual conditions of development occurs in the layer of 

 cells next outside the stele; and that this suberization, under the 

 usual conditions, may be considered an indication of the morpho- 

 logical boundary of the stele, but that it is subject to variation with 

 physiological conditions. Lang has concluded that the internal 

 endodermis of B. Lunaria is of physiological significance only, and 

 has suggested that its development is associated with the long leaf 

 gaps of the intermediate region of the rhizome. It is to be noted 

 that the apparent internal endodermis in injured specimens of B. 

 obliquum (fig. 6, E, F) occurs between masses of vascular elements 

 and points of injury. 



Of the stelar tissues, the tracheids and sieve tubes are incapable 

 of further growth. The remaining tissues are separated by these 

 into three groups: (1) pith, (2) cambium and adjacent parenchyma, 

 and (3) pericycle. The data given above show that all these three 

 tissues may produce vascular elements, either tracheids or sieve 

 tubes. Hence we may conclude that the production of vascular 

 elements by any stelar tissue is limited only by the capacity of the 

 tissue for further growth. 



The manner of that further growth of a stelar tissue varies with 

 the species. In Ophioglossutn pendulum, which has no secondary 

 thickening, the strands of xylem in the pith of an aberrant speci- 

 men were primary in origin. In Helminthostachys, no secondary 

 xylem is formed under the usual conditions of development; and 

 renewed growth of the stelar tissues, as in the case of branching, 

 produces an irregular secondary thickening of the stele without a 

 definite meristematic layer. ( >n the other hand, B. virginianum and 

 B. obliquum show very great development of secondary wood under 

 usual conditions. In both these species, renewed growth of the 

 pith, cambium, and pericycle manifested itself in part by the 

 formation of secondary xylem. Hence we may conclude that the 



