100 c.c., and exposed forthwith, one behind CuSO4, the other behind K. bichromate. No direct sunlight was allowed to fall on the cultures, cardboard shutters being used, and the mirrors took the light from the sky only. The day was hot and sunny, with heavy clouds occasionally and dull rainy afternoon, the following being the temperature, &c., records. The cultures were examined at 2 P.M., 5 P.M., 10 P.M., and 9 A.M. next morning, with results as given below: No germination had occurred in either culture at 2 P.M., nor even at 5 P.M.; but at 10 P.M. both had germinated, and the condition of affairs was as follows: In the blue culture the longest rods were 176 μ, and the shortest 8.8 μ, giving a mean of 13.2, which was about the average length. In the red culture, however, I found filaments 44 μ, 76 p, 110 μ, and even 150 μ in length. Mean of extremes = 97 μ. On leaving the cultures through the night, at about 12-13° C., and examining at 9 A.M. next day, the one over bichromate had filaments from 220 μ to 660 μ long, whereas none in the blue light were more than 88 u to 130 μ long. Since the variations in temperature (N.B.-The rapid and extreme variations only refer to the control cells, and were made for experimental purposes) only concern the exposure of the, as yet, ungerminated spores, we can hardly err in referring the retardation of the spores in the blue-light to the inhibitory action of the light rays. At 7 A.M. I sowed spores in gelatine-broth, and exposed forth with at an east window. The cells had a quartz floor, and a plate of glass covered with tin-foil was put over them to keep the sun off the top glass. One was over red glass, the other over blue, and neither received any but rays reflected through these glasses from the microscope mirrors. Each had a dummy cell by its side, arranged similarly, the temperatures of which ran as follows: The day was bright, and every care was taken to keep the direct sun's rays off by means of shutters, &c. At 4 P.M. both cultures were removed to the south window, where the temperature was 21° C., and kept so till near 7 P.M., at which hour it had fallen to 20° C. It slowly fell during the night, as shown by curve, to 19-21°. The table on the next page gives the results (see also Curves 34 and 35, p. 343): Here, again, the results seem definitely positive, and only to be accounted for as due to the light rays, and one must conclude thatwith resting spores at any rate the above exposure to reflected light through blue glass causes very pronounced retardation, suggesting that a little longer exposure (or a somewhat more intense light) would have inhibited the germination entirely. * There was one filament about 500 to 600 μ long, and this brought up the average, but the majority were not above 150 μ or so. Effect of Light from Blue Sky on Spores. I now made a new departure. Starting from the fear lest any heating up of the bichromate, &c., screens, and the passage of the solar rays through so many glass layers, &c., might affect the results, I arranged screens and cultures as follows: : Three large circular crystallisation dishes, 12 in. wide by 4 in. deep, were taken; they were of thin clear glass, with vertical walls and flat floor. These were supported, bottom down, each on four corks just large enough to clear the cover-slip roofs of my cells, with their hanging drops. 27 6pm. 7 |