i6 
Journal of Agricultural Research 
Vol. XXIII, No. I 
batatas Poir) were readily attacked, with a firm dryrot, and the pro¬ 
duction of a distinct rose-geranium odor that is always evident in soft- 
rot due to Rhizopus nigricans Ehr. (14, p. 341). White potato (Solanum 
tuberosum L.) decayed rapidly with exactly the same symptoms as those 
described by Pethybridge for Phytophthora erythroseptica Pethyb. ( 18 ). 
The pink color, though not evident when the tuber was first cut, developed 
in the course of half an hour’s exposure to the air. This was especially 
striking when first seen, because of its unexpectedness. It was followed 
by a change to dark brown as with the other species. Tomato fruits 
(Ly copersicon esculentum Mill), green and ripe, were rapidly attacked, 
with the spread of the fungus through the interior with brown dis¬ 
colorations. No aerial mycelium developed. Dasheen ( Colocasia anti¬ 
quorum Schott) corms were not attacked by the fungus, though the 
same moisture and temperature conditions prevailed as with all the 
others. Onion (Allium cepa L.) was not decayed, except slightly in the 
particular layer in which the inoculum was placed. 
The whole series was in duplicate, with a third specimen punctured, 
but not inoculated, as a control. All controls remained intact. Later 
the entire series was repeated with identical results. Reisolations of the 
organism into pure culture were made from all except the onion and the 
dasheen. Plate 12 consists of photographs of the different specimens, 
showing the nature of the decay produced. 
Temperature has a marked influence on the development of the organ¬ 
ism. Corn meal agar plates were placed in a series of Altmann con¬ 
trolled temperature incubators ranging from about 4 0 to 40° C., with 
intervals of from 2 0 to 3 0 . The cardinal temperatures, as indicated by 
extent of vegetative growth, were approximately as follows: minimum, 
13 0 ; optimum, 30°; maximum, 36°. It will be seen that this organ¬ 
ism is like the tropical forms in having very high temperature require¬ 
ments. This explains the facts noted elsewhere in regard to season of 
active parasitism. 
INOCULATIONS INTO OTHER PLANTS 
No very wide range of growing plants was inoculated, due partly to 
lack of time and partly to the unsatisfactory results of previous investi¬ 
gators. In this connection Wilson (30, p. 77) says : 
A comparison of the results published by the various authors tends to throw decided 
doubt upon the value of this method [cross inoculations] of delimiting species in this 
genus, as practically any species of Spermatophyta, which is in nature subject to the 
attacks of any Phytophthora, is likely under laboratory conditions to be more or less 
severely attacked by almost any other species. Indeed, some of the hosts recorded for 
various species of the genus are not known to harbor these fungi in nature. It would 
appear, then, that the parasitism of Phytopthora is of such a low order that it will not 
admit of their being differentiated into races as are certain of the Uredineae for example. 
To consider one case: Phytophthora cactorum (Lebert and Cohn) 
Schrot, originally isolated from a species of cactus, was later found in 
Japan and America (20) on ginseng and still later in Europe (31) and 
America (r, 28) on apple and pear. Such inoculations may be, however, 
of direct value in some cases, and a few were made with the rhubarb 
Phytophthora on hosts of closely related species to determine whether the 
signs, if any, produced on the plant would be the same as those caused 
by the fungus originally obtained from it. 
Castor bean (Ricinus communis L.) inflorescences were cut from plants 
and inoculated in the laboratory, as was done by Dastur with Phytoph¬ 
thora parasitica . Male and female buds were attacked and discolored, 
