MacMillan: OBSERVATIONS ON PTERYGOPHORA. 733 
gophora branch dichotomously and build a strong holdfast re- 
sembling that of Zessonéa rather than that of Vereocystzs. 
Each young hapteric branch, in cross section, shows the char- 
acteristic structure, a great central mass of parenchymatous 
tissue surrounded by an ill-defined cortical area with an hypo- 
dermal cambium. No pith is present and the growth in length 
and thickness of the hapteres proceeds solely by cambial ac- 
tivity. Inolder holdfasts distinct growth-rings appear—some- 
thing that was not seen in the holdfasts of Lessonza, and seems 
not to occur in the hapteric branches of /Vereocysézs, the indi- 
viduals of which are shorter-lived. The appearance of these 
rings of growth in the secondary cortical tissues of the holdfast 
seems to be due rather to rhythmic changes in the character of 
the cell contents than to regular successions of larger and 
smaller cells, concentrically arranged. As will appear, this 
character serves to distinguish to some extent between the 
growth-rings of the holdfast and of the stipe. In both organs 
the elements of the secondary cortex are arranged in extremely 
regular rows, as seen in cross section. This regularity of ar- 
rangement does not extend to the primary parenchymatous 
tissue of the hapteric branch, so that the appearance of a cross 
section of the older hapteres may be described as follows: At 
the center is a large more or less circular group of parenchy- 
matous elements regularly hexagonal in outline, varying in size 
between rather narrow limits. Towards the periphery this cen- 
tral tissue imperceptibly merges with the secondary tissue, the 
cells of which become more quadrate in outline and assume the 
characteristic position in rows which can be followed without 
break directly to the cambial zone which lies near the periphery 
of the organ. Inthe secondary tissue there are numerous rings 
of growth and the cross section of an old haptere, a centimeter 
or more in diameter, looks not unlike a section of stipe, save 
for the absence of the characteristic lenticular pith. This is 
altogether wanting in the hapteres. The growth-rings do not, 
however, appear to arise consistently through quite the same 
anatomical conditions as those of the stipe. Well-marked rings 
in the holdfast may exist without difference in the size of the 
elements of which they are composed. The optical appear- 
ance, therefore, is in all hapteres examined determined by dif- 
ference in the cell contents. A zone of cells will be formed in 
which the contents seem to be more dense. Outside a zone, in 
