MacMillan: OBSERVATIONS ON PTERYGOPHORA 735 
Pterygophora may safely be described as devoid of these 
canals. Thecross section of a young stipe shows the character- 
istic lenticular pith-web, composed of anastomosing filaments 
with numerous trumpet hyphe 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 Coniferee. 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 slight! «%rger lumina. That is to say, the occasion 
for the ringed ar ‘ance of the stipe is structurally quite com- 
