MacMillan : OBSERVATIONS ON PTERYGOPHORA 735 



Pterygo-phora may safely be described as devoid of these 

 canals. The cross section of a young stipe shows the character- 

 istic lenticular pith-web, composed of anastomosing filaments 

 with numerous trumpet hyphae intermingled. Chloroplasts 

 are abundant in this tissue and occur more or less sparingly in 

 the perimedulla. Surrounding the pith one finds the cells of 

 the cortical tissue very regularly hexagonal in shape, arranged 

 in remarkably perfect radial rows and diminishing gradually in 

 size towards the periphery. Chloroplasts are absent from most 

 of the cells of this tissue, but appear again, in the smaller 

 cells near the periphery. At about the depth at which chloro- 

 phyll becomes abundant the tissue is lacuniferous and the outer 

 cortex readily separates from the inner. The cells of the 

 outer cortex are generally not hexagonal, but cambial condi- 

 tions cause them to assume the rectangular outline in cross 

 section. The small densely colored cells of the epidermis and 

 hypodermis are uniformly quadrangular. Longitudinal sec- 

 tions through material of this age show the inner cortex to be 

 made up of prosenchymatous elements not pitted or armed and 

 the walls comparatively thin in the region near the pith, but 

 becoming thicker-walled and beginning to present the pitted 

 structure closer to the periphery. The cells of the outer cortex 

 seem to have a special capacity for dividing transversely and 

 periclinally in young material, but in older stipes they divide 

 radially with equal ease. In mature stipes the extraordinarily 

 regular radial rows of cells seen in cross sections may be ob- 

 served to originate from rows of cambial cells which have 

 divided radially in the outer cortex and have there established 

 the general radial arrangement of the tissues. 



Sections through the mature stipe show a structure of the 

 organ in cross section reminding one very much of the tracheids 

 and their arrangement in the Coniferae. The pits, however, 

 are not upon the radial faces of the elements, but upon the con- 

 centric. The cells are all of about the same size and stand in 

 rows radiating in a most regular fashion from the pith to the 

 circumference. There is often not the slightest difficulty in 

 observing that the appearance of growth-rings is due to the 

 gradual diminution in the diameter of the cells until they have 

 become distinctly flattened, followed abruptly by the production 

 of cells of slightly larger lumina. That is to say, the occasion 

 for the ringed appearance of the stipe is structurally quite com- 



