ENVIRONMENTAL FACTORS 



71 



It is well known that spores of bacteria, unlike the vegetative 

 cells, are extremely resistant to heat, — an exposure of one or two 

 hours at the boiling point often fails to kill the more resistant 

 forms. Likewise, it has been supposed that spores of fungi are 

 similarly more resistant than the vegetative condition. This has 

 not been found to be true in the case of Sporotrichum globu- 

 liferum} and it was demonstrated in my laboratory that spores 

 (conidia) of five forms — Aspergillus niger, Aspergillus flaws, 

 Penicillium sp., Botrytis vulgaris, and Rhizopus nigricans — differ 

 very slightly as to the thermal death point from that of the vege- 

 tative hyphse. 2 Nevertheless, some spores of even parasitic forms 

 are particularly resistant. It would appear that sclerotial-like struc- 

 tures or similar forms are also capable of withstanding high tem- 

 peratures, but there is no data which can be presented. 



Low temperatures. In general, fungi are able to withstand very 

 low temperatures. Few fungous spores are injured at o° C. It 

 will be found quite generally true that cultures of saprophytic or 

 parasitic organisms may be frozen solid in freezing mixtures with- 

 out unusual injury. The effects of winter conditions are not ordi- 

 narily such as to destroy fungous spores to any great extent. 



Light. The ultimate effect of light of different intensities upon 

 organisms may be manifest through injury, change of form, or 

 special stimulation. The immediate cause of the particular in- 

 fluence is always difficult to determine, as is true in cases of the 

 action of most external agents. A considerable number of in- 

 vestigators have studied the effects of light upon the living cells 

 of fungi and bacteria with regard to its injurious action, inhibition, 

 or stimulation of germination, and the effects upon growth and 

 reproductive processes. In general those organisms seem most 

 readily injured by light which are sensitive to many other exter- 

 nal stimuli. Pathogenic bacteria and certain hyaline fungi with 

 specially restricted life relations are soon killed by direct exposure 

 to sunlight. Some saprophytic forms are more resistant, and dark- 

 colored fungous spores or hyphae are far less influenced. Ward 

 made fresh sowings of Bacillus anthracis in nutrient agar in 

 Petri dishes, covering the dishes with glass or quartz plates, and 



1 Duggar, B. M. Bot. Gaz. 27 : 131-136. 1899. 



2 O'Brien, Abigail. Built. Torrey Bot. Club 29 : 170-172. 1900. 



