316 Profs. Percy Frankland and Marshall Ward. 



red glass, which cuts out all the hlue rays, at the temperature 

 given, in 10^ hours, amounts to from 144 to more than 160 times 

 the length of the spore, it is only 25 to 45 times its length in the 

 same period if exposed for six or seven hours of the time to light 

 passing through glasses (pale olive or ordinary) which transmit most 

 or all of the blue rays. Under the same conditions spores behind 

 glasses (blue and green) which act partly as shades which reduce the 

 intensity of the light (and in so far favour growth), and partly as 

 screens which so alter the composition of what light is transmitted 

 that it consists pf relatively large quantities of blue, show decided 

 retardation of the growth which in the given period amounted to 

 from 65 to 104 times the length of the spore act as might be 

 expected, and the amount of growth is somewhere between the 

 extremes. 



In the following experimental series these facts seemed to come 

 out still more prominently, principally perhaps because the tempera- 

 ture was somewhat higher and the insolation longer. 



The arrangements were exactly as before, but the culture under 

 pale olive glass had to be discarded, owing to partial drying up of 

 the drop, because the gelatine luting was incomplete. 



The spores were sown at 11 A.M., and the exposure began at 12 

 noon, the temperature being 16 C. The sun was bright and hot, 

 and was directed on to each culture at the commencement for five 

 minutes. An hour later, i.e., at a period when the swelling spores 

 would be just on the point of: germinating, another five minutes' 

 insolation was allowed to each, and so on through the afternoon, i.e., 

 five minutes at 2, 3, and 4 P.M. respectively. 



For the rest of the period the mirrors were carefully arranged, so 

 that only bright light from the blue sky or from brilliantly illumi- 

 nated clouds was allowed to fall on them. 



The temperature steadily rose to 18 19 C. about 1 P.M. to 21 

 22 C. at 2 P.M., and to 2324 C. between 2 and 3 P.M. At 4 P.M. it 

 had fallen to 19 C., and so down to 16 C. at 10 P.M., at which it 

 remained through the night. 



The first measurements were taken at 4 P.M., i.e., after the spores 

 had been sown five hours. As before, I examined each culture in 

 the order of its making, so that although the hours given in the 

 table are only the approximate mean times of the periods (about 

 half an hour) occupied in examining the whole series, they give the 

 correct interval in each case, whence no allowance need be made 

 for the minute increments of elongation during those periods (see 

 Curves 710). 



