1 5 8 Magnus. — On A ecidium gravcolens ( S hut t lew'). 
give a very characteristic appearance to the transverse sec- 
tions of the older stems of the witches’ broom. In these 
mycelial hyphae, which have a very small lumen, I have 
never observed the yellow colouring-matter of the Uredineae 
described by Eriksson (loc. cit.) in the mycelial filaments of 
the cambium, which he states are intracellular. I will at once 
remark that I have generally observed the yellow colouring- 
matter of Uredineae only in the mycelial filaments which are 
exposed to the light, never in those portions of the mycelium 
which are embedded so deeply in the tissue of the host-plant 
as not to be exposed to the light. 
As I have already stated elsewhere 1 , the spermogonia 
appear on the whole surface of the first leaves, which are 
developed in April and the beginning of May, and the aecidia 
appear between the spermogonia ; on the later leaves of the 
infected buds are found single larger or smaller groups of 
aecidia only, while the latest formed leaves are altogether 
free from the Fungus. At the end of April or the beginning 
of May a large number of these buds had already put out 
branches with long internodes. The leaves of these branches 
are free from the Fungus, as I have said. If longitudinal 
sections of these long branches be examined at the end of 
April or beginning of May, the hyphae in the pith will be 
seen growing in a longitudinal direction into the region of the 
merismatic tissue (Fig. j). These mycelial strands are inter- 
cellular, and occur in the actually dividing cells of the 
parenchyma of the pith. The cells around these mycelial 
strands are sometimes more elongated than the others, and 
remain for some time in this condition, while the neighbouring 
cells are undergoing transverse division (Figs. 2, 4). This 
intercellular mycelium often sends into these neighbouring 
parenchymatous cells haustoria of the same kind as those 
already described (Figs. 2, 4). From these longitudinal 
mycelial threads horizontal threads grow out laterally (Fig. 2). 
These are the threads which grow into the medullary rays, 
1 Verhandl. des Botan. Vereins der Provinz Brandenburg, Sitzungsberichte, 1875, 
pp. 87-89 (which was also published in Hedwigia-, 1876, No. I). 
