342 
Blackman. — On the Fertilization , Alternation of 
MYCELIUM AND DEVELOPMENT OF UREDOSPORES. 
Phragmidium violaceum. 
The uredospores appear on the leaves about June and replace the 
aecidia, which are only short-lived. After passing the aecidial stage the 
parasite appears to have gained greatly in energy, for the degree of infec- 
tion is now much greater 1 . The mycelium in the leaf which gives origin 
to the uredospores shows, naturally, paired nuclei like the aecidiospores 
from which it was derived. 
The details of uredospore-formation were not investigated in the leaf, 
but from some patches on older stem-portions where the mycelium was 
perennial and gave rise to uredospores early in the year, even before the 
aecidia were developed on the leaves. These patches were found to be 
much more favourable objects of study than those on the leaves, the 
general form of which has been figured by Sapin-Trouffy. The perennial 
mycelium was found to form a layer of considerable thickness, in which 
even thin sections show a considerable number of the nuclei arranged in 
pairs (Fig. 78), but as the two nuclei of these cells often separate for some 
distance, the paired condition cannot always be observed. A number of 
the hyphae penetrate the cells of the host, thus acting as haustoria 
(Fig. 99), but they did not appear to have that special relation to the 
nucleus of the host-cell described for several cases by Sapin-Trouffy. 
The stalked uredospores are borne on somewhat rectangular cells 
which may be termed basal cells. They grow up from the free surface 
of mycelium and form a regular layer (Fig. 79). These cells are usually 
vacuolate, and show two nuclei which are larger than the nuclei of the 
mycelial cells and exhibit each a well-marked nucleolus and granular 
chromatin. The uredospore arises from the basal cell as a binucleate 
outgrowth (Figs. 80, 81), which soon becomes of a somewhat oval shape. 
The two nuclei then undergo the process of conjugate division (Fig. 82) 
and the outgrowth becomes divided into two cells (Fig. 83), the upper 
increasing much in size and forming the uredospore, the lower remaining 
narrow, but elongating later and forming the stalk. 
The wall of the uredospore becomes much thickened, but a very 
definite pit through which there is distinct protoplasmic continuity con- 
nects, for some time, its cavity with that of the slightly thickened stalk 
(Fig. 83 a). In the mature state, however, before the uredospore separates 
from the stalk, the pit becomes obliterated. 
1 The discovery of a process of fertilization is, of course, a confirmation of the interesting view, 
put forward by Arthur (1, 2), on other grounds, ‘that the aecidium is a device to restore vigour to 
the fungus.’ 
