Oct. ii, 1915 
Perennial Mycelium in Species of Peronosporaceae 65 
in the patch and why plants growing near each other should be infected 
in some cases and not in others. 
As the host is a perennial, as infection by Peronospora viciae is sys¬ 
temic, and as oospores are produced only sparingly, if at all, on Vicia 
sepium , 1 it seems very probable that the mycelium survives the winter in 
the living tissues of the host. 
FLASMOPARA HALSTEDII 
In the spring of 1911 Plasmopara halstedii was found to be very 
abundant on some young plants of Helianthus diversicatus about 6 inches 
high. The plants were somewhat dwarfed, chlorotic, and well covered 
with conidiophores, giving every evidence of systemic infection. The 
location of the infected plants was 
marked and observations made during 
the winter and spring of 1912. 
Fourteen of the plants that were very 
generally infected were staked, and on 
January 4, three of these were chopped 
out of the ground and transplanted in the 
greenhouse in exactly the same way as 
were the Lepidium plants infected with 
Peronospora parasitica. Each of these 
rhizomes produced a chlorotic shoot 
which was covered with spores of Plas¬ 
mopara halstedii. On March 4 four more 
were brought into , the greenhouse. One 
of these rotted in the soil, but each of 
the others produced a shoot, which 
showed infection as soon as it appeared 
above ground. The remaining seven of the fourteen staked were left in 
the patch and kept under observation. On May 10, when they were 3 
to 6 inches high, all were found to be infected with Plasmopara halstedii , 
except one plant, which was entirely free from infection, as were many 
others in the immediate vicinity. Two of these plants were now dug 
up, and portions of the stems at their junction with the rhizomes were 
fixed in various strengths of Flemming's killing fluid. Paraffin sections 
cut from this material and stained showed abundant mycelium in all 
parts of the stem except the fibrovascular bundles, the mycelium being 
entirely intercellular with globular haustoria extending into the cells, 
as shown in figure 1. The presence of the mycelium in the stem at its 
junction with the rhizome shows that the infection was systemic and 
probably came from the rhizome in the beginning. 
1 The writer searched many times in the tissues of all stages of maturity for resting spores, but without 
success. 
Tig. i.—A cross section of a stem of Helian - 
thus diversicatus which is infected with 
Plasmopara halstedii . The mycelium is 
shown in the cortex at the junction of the 
stem with the rhizome of the host. 
