DISCUSSION OF INCUBATION TESTS. 93 



Study of the figures given shows a progressive increase in growth 

 from tin- coldest to the warmest compartment. Examination of the 

 cultures showed thai at the lower limits of growth very many species 

 produce colored fruit verj slowly at temperatures at which vegetative 

 mycelium is still developed quite rapidly. There often results, 

 therefore, in cold temperatures a disproportionate growth of white 

 mycelium and a tardy development of colored conidia, which often 

 a I Fret'- the appea ranee of the resulting colony considerably. Cultures 

 grown under such conditions would be difficult to identify in many 

 cases. The forms which grew most rapidly at .".7° C. either failed to 

 grovi at the colder temperatures or responded very slowly. The large 

 majority of the species, and especially those most commonly found in 

 food materials, are seen to begin fairly rapid growth at temperatures 

 within a few degrees of the freezing point. When taken from the ice 

 thermostat all cultures which had failed to produce normal colonies 

 grew quickly to typical appearance. There was, therefore, no injury 

 attributable to continuation for 29 days at Low temperature. The 

 general effect of low temperatures upon these species is the suspension 

 of or the reduction of the rate of development. In many cultures 

 the beginnings of growth were difficult to detect and in most eases an 

 exactly critical temperature is not determinable, since cultures not 

 showing any growth in one week seem gradually to adjust them- 

 selves to conditions and produce mycelium in the succeeding weeks. 



Eustace 8 has recorded that one of these species (P. expansum 

 Link of this paper) will produce rot in storage apples where the 

 temperature of the room as recorded does not rise above 32° F. 

 (0° C). When the time was extended to two months Petri-dish 

 cultures under the same conditions produced small colonies. The 

 experiments here recorded tend to suggest that very little growth 

 will occur in most species at temperatures nearer than 2° C. to the 

 freezing point, although many of them will germinate. Unpub- 

 lished records of the temperatures of apples in storage, furnished 

 by Mr. ('. I). Jarvis, of this station, showed that the flesh of apples 

 in storage was constantly from 1 to 2 degrees at least above that of 

 the room. Allowing for the conductivity <>f the thermometer itself, 

 the difference is probably somewhat greater. Both series of data 

 indicate, however, that storage 1 temperature to exclude fungous 

 grow th must be close to the freezing point. It is clear that low tem- 

 peratures (above freezing) merely restrain growth, not entirely 

 prevent it. It is also clear thai by restraining the production of 

 colored fruit many colonies would be rendered inconspicuous (al- 

 though widely growing), thus accounting for the complaint so often 

 heard with reference to dairy products taken from the refrigerators, 

 that they turn green with mold very quickly. 



