THE MORPHOLOGY OF THE PERIDIAL CELLS IN 
THE- ROESTELIAE? 
FRANK DUNN KERN 
(WITH PLATES XXI AND XXII AND TWO FIGURES) 
While making a study of the morphological characters of various 
species of Roestelia, attention has been especially attracted to the 
peridial cells. They are much more characteristic than are the roes- 
telial spores, and so strikingly different, except in two known cases, 
from the peridial cells of the aecia of pucciniaceous species that they 
are at once conspicuous upon the most cursory examination. The 
two exceptions just cited are Aecidium Blasdaleanum D. & H. and 
Aecidium Sorbi Arth., which are classed with the Roesteliae on 
account of their life histories, but which have the morphological 
characters of the pucciniaceous aecia and are therefore not included 
in the discussions in this paper. The taxonomic importance of the 
peridial cells in defining the species of Roestelia has been ably pointed 
out by Dr. Ep, FiscHer,? and a number of American species have 
been figured and described? in considerable detail by him. F1scHER 
took into account only the surface sculpturing on the cells, but aside 
from this there are a number of other features of the morphology 
which seem worthy of consideration. The microscopical structure 
is described with some detail in this paper, with the hope that it may 
be of interest. 
The manner in which the individual cells are joined together 
to make up the peridium is one of the first characteristics worthy of 
mention. If a bit of the mature peridium of almost any of the species 
is mounted in water for a microscopical examination, the cells are 
usually seen separated from one another, or perhaps a few short 
chains made up of cells attached together at the ends remain. In 
case the cells do not separate while the mount is being prepared, a 
* Read before the Botanical Section of the American Association for the Advance- 
ment of Science at the Baltimore meeting, December 29, 1908. 
2 Zeit. f. Pflanzenkr. 1:271. 1891. 
3 Hedwigia 34:3, 4.- figs. 1-10. 1895. 
445] . [Botanical Gazette, vol. 49 
