June i6, ^ 6)23 
Watery-Rot of Tomato Fruits 
899 
TabIv^ II .—Relation of temperature to growth and infection by Oospora lactis parasitica 
Temperature. 
Growth on 
culture 
media.® 
Infection of 
pricked 
tomato 
fruits. 
1 
Germina^ 
tion of 
spores. 
Maximum. 
38.5 
30. 0 
2. 0 
"C. 
37 - 5 
30. 0 
2. 0 
“C. 
38.5 
30. 0 
2. 0 
Optimum. 
Minimum ^ . 
« Carrot agar and glucose agar. 
b The experiments on the minimum temperature were run about a month. 
ei^fe;ct on the host 
ACTION ON THE CUTiCbE 
It was shown in the inoculation experiments described above that this 
fungus is unable to infect uninjured tomato fruits except through the 
stem scar or other similar areas not covered by the cuticle. This is 
also illustrated in Plate i, A. The fungus lay in masses on the surface 
of the fruit but was unable to penetrate it. However, when once inside 
the fruit it invaded the epidermal cells quite readily. 
ACTION ON THE PROTOPLASM 
Invasion of the host cells is soon followed by a gradual consumption 
of their protoplasmic contents. Some of the steps in this process are 
illustrated in Plate i, in which B and C show an early stage, D a medium 
early stage, and E-J late stages. This action of the fungus on the 
protoplasm of the invaded cells is quite evident soon after the pene¬ 
tration of the wall, as it causes dissolution of the protoplasm in advance 
of the growing tip (PI. 3, R). These transparent areas, or digestion 
vacuoles immediately surrounding the filaments, are shown more fully 
in Plate i, B~D, and Plate 3, U. It would seem from these figures that 
the proteolytic enzym secreted by the fungus acts chiefly in the region 
of the growing tip. There was apparently no preference for the nucleus, 
as it often remained intact after most of the other cell contents had 
disappeared. 
Quite different results were obtained with the ground dried organism, 
the filtrate, and the alcoholic precipitate from the filtrate. Repeated 
experiments with these substances produced no visible effects on the 
protoplasm. The failure to obtain a proteolytic action with any of 
these substances may be due to a rapid deterioration of the enzym, to 
inhibitors, or to lack of suitable technic. 
ACTION ON THE MIDDLE LAMELLA 
The growing fungus, as shown in Plate i, dissolves the middle lamella 
slowly, causing the loss of cell coherence. This loss of coherence and the 
breaking up of the fungus filaments into their individual cells produce 
the extremely watery consistency which distinguishes this rot from other 
softrots in which the fungus filaments remain intact and hold the host 
cells together. A similar action was produced on the middle lamella 
by the ground dried organism, the extract from the ground dried organ¬ 
ism, the filtrate, and the alcoholic precipitate from the filtrate of cultures 
2 to 3 days old, but this activity diminished as the age of the culture 
