37 
Sexuality of the Uredineae . 
The material was fixed in Flemming’s weaker fluid or in acetic 
alcohol (20 or 25 per cent. sol. of the acid in absolute alcohol). The 
latter fluid does not fix so well as that of Flemming, but is much more 
penetrating, and was always used when an air-pump was not available ; 
without the use of such an instrument watery fluids will not satisfactorily 
fix the portions of leaves. Bendas iron-haematoxylin followed by a one 
per cent, watery solution of Congo-red, as already described ( 2 ), was 
found the most satisfactory stain. 
In addition to the cytological observations mentioned in the earlier 
paper (1), the general morphology of the aecidium has been investigated 
by De Bary, Neumann (6), and Richards ( 7 ). 
Uromyces Poae, Raben. 
This is a heteroecious eu- form with its spermogonial and aecidial 
stage on Ranunculus Ficaria . Material was obtained in April and fixed 
in acetic alcohol. 
The vegetative mycelium of the Fungus is found ramifying among 
the cells of the leaf and petiole, and occasionally of the young fruit. 
The hyphae exhibit single nuclei, usually in separate cells, as was 
observed earlier by Sapin-Trouffy (8). 
The spermogonia appear early on the upper side of the leaf and have 
the typical flask-shaped structure, being very similar to those of Puccinia 
graminis . The spermatia (PI. Ill, Fig. 10) have the large nucleus and 
the reduced cytoplasm which has been pointed out in the earlier paper 
( 1 ) as characteristic of these cells throughout the group. They take 
no part in aecidium development and are, as usual, without apparent 
function. 
The first indication of the young aecidium is a mass of tangled hyphae, 
which develops directly below the epidermis on the under side of the 
leaf ; in the petiole this mass may be placed a little deeper. The group 
of hyphae increases in size and soon shows a differentiation into two 
sharply marked portions, a lower consisting of a mass of closely packed 
hyphae composed of short, uninucleate cells with dense contents, and 
an upper consisting of large irregular hyphae which are almost completely 
empty (Fig. 1). The large empty cells seem to be derived, at least in 
part, from the lower small-celled hyphae with dense contents, for cells 
cut off from the latter can be seen enlarging and losing their contents. 
The nuclei of the cells with granular contents contain in the resting 
state a very well marked nucleolus, but the chromatin is very small in 
amount, and both it and the nuclear membrane stain with great difficulty. 
This nuclear structure is characteristic of all the cells of the aecidium, 
so that in ordinary lightly stained preparations the nucleus appears as 
a deeply staining large granule, the nucleolus, surrounded by a light 
