Igto] KERN—PERIDIAL CELLS IN. ROESTELIAE 447 
thomboidal (figs. 3, 4, 10) is a more accurate description; or where the 
length is very great comparatively, the obliqueness at the ends is incon- 
spicuous and they may best be described as linear (jig. 7). In face 
view, which is the longitudinal tangential view, length and breadth are 
the dimensions in the plane of vision. The cell may be regarded as 
having two faces, the one which is to the outside, and the one which 
is to the inside as it is in place in the peridial wall. The distance from 
the outer face to the inner face constitutes the thickness of the cell. 
In considering shape in face view it makes no difference which face 
is turned toward us. The cells of some of the species are not easily 
seen in face view, but of those that will lie so as to be readily examined 
the majority do not have the side walls parallel, but vary from lan- 
ceolate or broadly lanceolate (fig. 16) to polygonal-ovate or poly- 
gonal-oblong (fig. 9b). Most of the cells are more or less narrowed 
both above and below (fig. 17b). There is one species, G. Botry- 
apites (Schw.) Kern (R. Ellisii Peck), which does not conform to 
any of the shapes mentioned. It has cylindrical hypha-like cells 
which are sometimes irregularly bent (fig. 12). 
The accompanying table will serve to show the variation in size 
of the cells and in thickness of the walls. In the measurements given 
an attempt is made to make some allowance for the variation within 
any particular species, it being the case in most instances that the 
cells near the apex are proportionately shorter. G. Bermudianum 
(Farl.) Earle, the only autoecious species known to exist, has the 
shortest cells of any examined (fig. 1). The maximum length is 
three to four times greater than the minimum, and is found in the 
cells of R. transjormans Ellis (fig. 7), a species developing in the leaves 
and fruit ef Aronia arbutijolia (Pyrus arbutifolia). In most of the 
Species the breadth is greater than the thickness, but in three or four 
(nos. 9, 14, 15, 16 in the table) having especially firm peridia, which 
do not become much split or lacerated, the reverse is the case. 
With respect to thickness of walls, the general type of peridial 
cell has inner and side walls rather thick with outer wall rather thin. 
The side walls appear to be about equal in thickness with the inner 
wall in the species where the inner wall is only moderately thickened 
(text fig. 2, a, b). In some very thick and proportionally narrow 
cells, where the inner wall is excessively thickened, the side walls 
