Jan. 6,1923 
A Phytophthora Footrot of Rhubarb 
17 
but no fruiting of the fungus occurred. Further inoculations were made 
with zoospores and with mycelium from a culture, on the young growing 
inflorescences and leaves of castor beans, numbering six in all. Definite 
signs of infection resulted, which were, however, confined to small, 
irregular spots and did not spread. No fruiting of the fungus occurred, 
even though high humidity and a favorable temperature were main¬ 
tained. Six inoculations each similarly made on young tomato plants 
(Lycopersicon esculentum) 
and on young dasheen 
leaves (Colocasia antiquo¬ 
rum) failed to produce in¬ 
fection. 
HISTOLOGICAL STUDIES 
The time available for the 
study of the problem was 
too limited to permit of go¬ 
ing deeply into the matter 
of penetration and infection 
of the host. One mount 
was made after the manner 
described by Vaughan (27) 
of a portion of the epidermis 
of a rhubarb stalk, at a point 
recently inoculated with 
zoospores. This showed 
hyphae arising from germi¬ 
nating zoospores, growing 
along the surface, and in 
one case, at least, penetrat¬ 
ing a stoma. Whether this 
is the regular method of 
penetration is not com¬ 
pletely worked out. After 
entering the host, however, 
the fungus is principally 
intercellular. Figure 3 con¬ 
sists of semidiagrammatic 
camera-lucida drawings of 
free-hand cross sections of a 
rhubarb leaf stalk show¬ 
ing intercellular hyphae and a haustorium. Cell wall penetration 
takes place occasionally by means of a fine constriction, enlarging 
after penetrating, to normal size. Figures I and J of Plate 10 show 
such penetration, as well as the intercellular hyphae. The sections 
from which these slides were made were cut from a block taken from 
the base of the stalk shown in Plate 1, B. In the only cases of such 
penetration actually observed the fungus did not continue to grow 
through the cell, but appeared to develop into haustoria, both the short, 
button-shaped and the finger-like forms having been seen, such as those 
pictured by Dastur for Phytophthora parasitica ( 10 , PL III). The fixed 
material was killed in Fleming’s weak killing fluid, sectioned 6 jx thick, 
and stained with Pianeze III B stain (27). Another stain found by the 
author to differentiate quickly the fungus within the host was a new 
20516—23 - 2 
Fig. 3. —Semidiagrammatic camera-lucida drawing showing 
intercellular mycelium and penetration of a cell wall. One 
space in the scale represents io 
