898 
Journal of Agricultural Research voi. xxiv. No. n 
Germination of the spores may start from the end (Pi. 3, I, L), from 
the side (PI. 3, J, K), or from a comer (PI. 3, I, M). Development from 
a comer of the cell is quite similar in point of origin to the development 
of the branches shown in Plate 3, A. 
COMPARISON WITH OOSPORA LACTIS 
The Oospora obtained from rotted tomato fruits shipped from the 
Gulf States was compared morphologically with the Oospora lactis that 
commonly grows on the surface of tissues in the cracks of ripe tomatoes; 
with two cultures of O. lactis received from Dr. Charles Thom, one 
isolated by him from pickle scum, the other sent to him from Germany; 
and with an Oospora isolated from green tomato fruits affected by 
watery-rot at the Government Experimental Farm, Arlington, Va. 
The two Oosporas causing watery rot and the one from Germany did not 
always break up into their cells so readily and completely as those from 
the cracks of ripe tomatoes and from pickle scum, but this habit varied 
with the age of the culture and with the kind of culture medium used. 
Aside from this difference, which was not constant, and slight differences 
in quantity of mycelial growth, there were no peculiarities, except in 
parasitism, by which one form could be distinguished from the others. 
The Oospora received from the Gulf States and the one obtained from 
green tomato fruits at the Government Experimental Farm reproduced 
the watery-rot in a large percentage of the fruits inoculated, but the 
others appeared to have no such parasitic action on tomato fruits. It 
would seem, therefore, that the Oospora causing watery-rot of tomato 
fruits, both in the Gulf States and at the Government Experimental 
Farm, is a physiological form of O. lactis. Consequently we have 
given it the trinomial O. lactis paralitica, form phys., to distinguish it 
from the parent species. As it is indistinguishable morphologically 
from O. lactis, it needs no further description. 
It would be interesting to know how this form compares with the 9 
varieties of Oospora lactis that Schnell { 8 ) grew on sliced potato tubers, 
but as he made no inoculations on tomato fruits an accurate comparison 
of their parasitism is impossible. Six of the 9 varieties grown on sliced 
potatoes, 4 of which grew also on sliced cucumbers and 2 on plums, 
produced a discoloration of the potato tissues which would distinguish 
them from the form isolated from green tomatoes. Two of the others 
produced slimy colonies on sliced potatoes—a character not obtained with 
the watery-rot fungus. The remaining strain, viz, Oid. 1. 557, made a 
feeble growth on potato tubers, agreeing in this respect with the one 
isolated from tomato fruits affected by watery-rot, but this has no sig¬ 
nificance with reference to its parasitism on tomato fruits. 
TEMPl^RATURK R^nATlONS 
The effect of temperature on growth and infection by Oospora lactis 
parasitica is shown in Table II. 
The minimum temperature obtained for germination of the spores, 
for growth of the mycelium, and for infection of pricked tomato fruits 
was approximately 2° C., the optimum temperature 30"^, and the 
maximum 38.5°, except for infection of fruits, which was 37.5°. As 
there was a difference of 1° to 2° between the temperatures of adjoining 
chambers and some fluctuation within each chamber, these temperatures 
are only approximately correct. 
