RHIZOPUS EOT OF STRAWBERRIES m TRANSIT. 7 
PHYSIOLOGY OF RHIZOPUS NIGRICANS. 
CHARACTER OF THE ROT PRODUCED. 
The rot produced in strawberries by Rhizopus nigricans differs 
from that caused by any other organism the writers have observed 
and has been briefly described in an earlier paper (13). Its chief 
characteristic is the rapid collapse of the berry, with the loss of 
much juice. So great is this loss that the juice often drips from 
boxes or crates containing strawberries rotted by Rhizopus, and this 
has given rise to the name " leak " applied to this type of rot by ship- 
pers and dealers. F. L. Stevens (12) has recognized Rhizopus as 
the cause of this type of rot in strawberries. 
HUMIDITY RELATIONS. 
In investigating the humidity relations of this fungus in its attack 
on strawberries, a method already described by one of the writers (14) 
was employed. Briefly, the method consists in using a series of desic- 
cators filled with mixtures of sulphuric acid and w T ater in various pro- 
portions. From the specific gravity of the acid the relative humidity 
and the saturation deficit of the air in the desiccator were calculated. 
Repeated experiments, using partly decayed berries received in 
shipment, as well as sound Klondikes and Missionaries inoculated 
with Rhizopus nigricans, proved that the fungus will destroy the 
strawberry as quickly in a very dry atmosphere, even under concen- 
trated sulphuric acid, as in a moist or saturated atmosphere. Certain 
differences in the attack of the fungus on the berry under various 
humidities have been noted (13). The important fact in this con- 
nection is that when the fungus is once inside the strawberry no 
amount of external drying is sufficient to stop its development. The 
moisture contained in the fruit will permit the fungus to grow suffi- 
ciently to destroy the berry. 
TEMPERATURE RELATIONS. 
The temperature relations of Rhizopus nigricans have recently been 
studied by two investigators. Hanzawa (8) studied the temperature 
relations of various species of Rhizopus and used these relations as 
criteria for separating the genus into sections. He places Rhizopus 
nigricans in the section characterized by having no growth at 37° C. 
(99° F.). He found that this species was able to grow and produce 
sporangia at temperatures as low as 8° to 10° C. (46° to 50° F.). 
Miss Ames (1) included Rhizopus nigricans among the storage-rot 
fungi whose temperature relations she investigated. She found that 
at 9° to 10° C. (48° to 50° F.) some growth occurred, although at 
this temperature the fungus was unable to mature sporangia within 
one month. Maximum growth occurred at 36° C. (97° F.), good 
growth at 37° and 40° C. (99° and 104° F.), and no growth whatever 
