382 Profs. Percy Frankland and Marshall Ward. 



At 3.15 i.e., after five honrs' exposure the red culture had 

 grown considerably more than the blue one, although, so far as there 

 was any difference of temperature at all, it favoured the blue 

 culture. The filaments were too long, and too much curved to 

 measure, but there was no doubt as to the increased growth. 



Spores sown in normal gelatine at 10 P.M. on November 17, and 

 kept in the dark at 13 C., had germinated to rodlets averaging 

 9 12 fi long at 8.30 A.M. on November 18, when two cultures were 

 exposed to the clear blue sky on a mirror to the north and out of the 

 sun. The day was cold and very fine. Each culture was covered by 

 a black match-box screen, and had a thermometer control by its side 

 treated exactly like it. One culture had ruby glass over it, the other 

 blue; the latter was slightly in advance, i.e., had some slightly 

 longer rodlets. In order to be on the safe side I chose the culture 

 which had a slight advance if anything for the blue. 



The following table (p. 383) summarises the results of measure- 

 ments, and the temperatures. 



It is not difficult to translate these records. At the very low tem- 

 perature used growth was extremely slow* in both cases ; neverthe- 

 less the temperature was above the minimum, and the red glass 

 screen enabled it to go on as usual, because the inhibiting blue- violet 

 rays were cut off, whereas behind the blue glass these rays carried 

 on their destructive work, and the rodlets did not grow at all after 

 the first hour or two. 



A word of explanation is necessary, perhaps, regarding the slight 

 discrepancies between the measurements in the blue. 



Each drop had about 20 spores in it. In taking the successive 

 observations, two sources of (minute) errors exist : one is, that no 

 doubt the measurements, even of the same rodlet, are not perfectly 

 accurate it is easy to see how one could go wrong to 0'25, or even 

 0'5 of a fi the other is that one does not always find the same six or 

 eight rodlets, however carefully one tries. My practice is to seek for 

 the same, but to take care that every drop is thoroughly overhauled 

 for the biggest and the smallest rodlets. 



On the whole I think it will be admitted that the measurements 

 correspond very well, and that the averages are very good. 



At 9.15 P.M. the temperature was falling for the night, and it went 

 down to below 9 C. before morning, rising again slowly after sunrise ; 

 this explains the still slow growth of the red culture. 



At 8.30 A.M. I put both cultures into the incubator at 22 C., to 

 see if a rise of temperature would make any difference as regards 

 the dormancy of the blue culture. 



The result was that while the red culture had filaments from 40 to 

 300 y long by 12.30 noon, the blue one showed no further signs of 



* The doubling period would seem to be 360 400 minutes, or even longer. 



