une i6, 1923 
Watery-Rot of Tomato Fruits 
901 
spores that settle in the cells as well as the penetration of the wall and 
the effects resulting from it are easily observed by means of the micro¬ 
scope. Some short germ tubes lying near a wall and approaching it 
perpendicularly go directly through it without the use of any support or 
anchorage to increase their pressure. The opening made in the first 
half of the wall is a hole, not a basin or general depression such as would 
be produced by pressures, although the second half of the wall, i. e., the 
wall of the cell undergoing invasion, is sometimes pushed back. When¬ 
ever an invading filament completely fills the hole in the first half of the 
wall it attains a certain amount of anchorage which no doubt enables it 
to make some use of its growth pressure. This causes the second half 
of the wall to bend back before the filament has passed through it (PI. 3, 
P, T), but it is not essential to the penetration. Moreover, this bending 
is usually absent, because the hole made in the first half of the,wall, as 
shown by focusing sharply with the microscope, is usually a little larger 
than the filament (PI, 3, V). It is also destitute of radiating cracks or 
fragments such as would be likely to accompany the bursting of the wall 
by pressure. By pressing the cover slip with a needle so as to produce 
vertical and lateral movements the angle between a germ tube and the 
wall through which it has passed may be varied more than 90^^. This is 
caused by the pressure of the liquid against the filament, which changes 
its position in the wall without bending it at the edge of the hole. The 
two ends of such a filament usually move in opposite directions, especially 
when the part extending through the wall is three or four times as long 
as the part in the original cell. If the filament were rigidly fixed in the 
wall, the angle between it and the wall would not change unless the 
filament were bent at the edge of the hole. Moreover, an occasional 
filament can be made to slide in the hole. These phenomena are possible 
only when the hole is larger than the filament. In view of these facts, 
it would seem that this fungus invades the cells by means of a cellulose¬ 
dissolving enzym (cellulase) secreted by the growing tips while in con¬ 
tact with the wall. 
COMPARISON WITH BACILLUS CAROTOVORUS 
As this Oospora and Bacillus carotovorus ^ cause similar rots of tomato 
fruits, a comparison of their effects on the host is interesting. Oospora 
invades the cells and destroys the protoplasm before it causes much 
separation of the walls (PI. i, B-F). Although it is also found in the 
intercellular spaces, it apparently makes little use of them except as 
passages. Bacillus carotovorus^ on the other hand, remains in the inter¬ 
cellular spaces until it destroys the middle lamellae of the adjoining cell 
walls (PI. 2, A-D) and enters the cells usually after it has destroyed 
their coherence. That an earlier entrance is sometimes effected, how¬ 
ever, is evident from Plate 2, E. In later stages (Pi. 2, F-H) it not 
infrequently fills the cells. 
Knzym versus pressure 
If we assume that the penetration of the cuticle by all fungous para¬ 
sites is by “sheer mechanical presssure,” as concluded ior Botrytis drierea 
by Brown {4, 5) and by Blackman and Welsford (j) and for Sclerotinia 
3 An excellent history of the work done on the softrots of vegetables (also tomato) caused by the Bacillus 
carotovorus QTonp of organisms is published in “An Introduction to Bacterial Diseases of Plants,” by Erwin 
F. Smith (9). 
