DISEASES DUE TO FUNGI 59 
Dastur in India, during 1913, as causing a disease of the 
castor bean. In 1917 Sherbakoff (43) described “‘ buckeye”’ 
rot of tomato fruits as caused by a new species of Phytoph- 
thora—Ph. terrestria—which he also found attacking 
citrus trees and lupins. In pure culture tests it appears 
that Ph. terrestria is the same as Ph. parasiiica, the latter 
name having priority. It is highly probable that Ph. 
parasitica is a universal organism considerably more 
important than is at present imagined. Phytophthora 
cryptogea was first described by Pethybridge and Lafferty 
(37) in 1919 as the cause of tomato foot rot. From 
inoculation experiments they concluded that it produced 
the same kind of disease in the potato, Giulia tricolor, and 
elm seedlings. It was also found attacking the petunia, 
cineraria, aster, and wallflower. The genus Phytophthora 
develops non-septate thin-walled hyphe of a relatively 
large diameter and characteristic appearance. It 
produces egg-shaped conidia or sporangia, from the inside 
of which are liberated a number of active zoospores, each 
of which is supplied with two lash-like processes or 
cilia, enabling it to swim away in a film of moisture. 
Thick-walled vegetative cells, or chlamydospores, are also 
produced as well as thick-walled oospores, the product 
of sexual fusion. It is by means of the zoospores that 
the disease is able to spread rapidly. The zoospores 
settle down against the outside of the plant and produce 
germ tubes which enter the tissues. The thick-walled 
chlamydospores and oospores are able to resist abnormal 
conditions and so tide over the barren season or other 
adverse conditions. Ph. cryptogea and Ph. parasitica are 
closely allied species, differing only in minor details. 
Perhaps the best way of distinguishing between them 
is provided by the different way in which the two species 
produce sporangia. In Ph. cryptogea the stalk or spor- 
angiophore grows up through the old sporangium after 
the zoospores have been liberated, and produces a second 
sporangia beyond ,the old one, and this process may 
be repeated several times (Fig. 6). In Ph. parasitica 
