18 



MASS. EXPERIMENT STATION BULLETIN 183. 



It is apparent from these tests that spores germinate at any tempera- 

 ture between 8° and 36° C. Between 12° and 30° the percentage of 

 germination was almost total, ranging from 95 to 100 per cent, (all 

 marked 95 per cent, in the table). Within these Umits there was prac- 

 tically no variation of percentage due to temperature. In other words, 

 if the optimum temperature is to be determined by percentage germina- 

 tion alone, it is very wide. Below 12° the percentage drops off rapidly 

 until at 8° to 9° we get but 1 per cent, in twentj'-four hours. Germina- 

 tion ceases altogether below this. Between the temperatures of 31° and 

 36° it is difficult to express the effects of temperature in percentages. 

 Not only is germination erratic, varying greatly in slides apparently 

 treated alike, but it may also be so abnormal that it is difficult to de- 

 termine just what constitutes germination. The spores assume peculiar 

 shapes by the development of knobs or, more commonly, globose swellings 

 twice the diameter of the spores. These vary in number and location, 

 but most frequently they are on the ends of the spores. Very slender 

 unbranched germ tubes may grow for a time from these. The percentage 

 of spores affected does not gradually diminish to form a regular curve. 

 Thus, in one test at 36°, 70 per cent, were affected in this way. But 

 at 37.5° there was no germination or change in the spores which could 

 be detected with the microscope. The effect of temperature variation 

 is more apparent in the time required for germination to begin than in 



