[224] Ewald, W. F., _Science_, 1913, xxxviii., 236. It is of importance for the theory of the identity of the heliotropism of animals and plants that in the latter organisms the law of Bunsen and Roscoe is also applicable. This had been shown previously by Fröschel[225] and by Blaauw.[226] In the following table are given the results of Blaauw’s experiments on the applicability of the Bunsen-Roscoe law for the heliotropic curvature of the seedlings of oats (_Avena sativa_). The time required to cause heliotropic curvatures for intensities of light varying from 0.00017 to 26520 metre-candles was measured. The product _i t_, namely metre-candles-seconds, varies very little (between 16 and 26). [225] Fröschel, P., _Sitzungsber. d. k. Akad. d. Wissensch._, Wien, 1908, cxvii. [226] Blaauw, H. A., _Rec. d. travaux botaniques Neérlandais_, 1909, v., 209. TABLE VII ---------------+--------------+---------- I | II | III _Duration of | _Metre- | _Metre- Illumination_ | Candles_ | Candles- | | Seconds_ ---------------+--------------+---------- 43 hours | 0.00017 | 26.3 13 " | 0.000439 | 20.6 10 " | 0.000609 | 21.9 6 " | 0.000855 | 18.6 3 " | 0.001769 | 19.1 100 minutes | 0.002706 | 16.2 60 " | 0.004773 | 17.2 30 " | 0.01018 | 18.3 20 " | 0.01640 | 19.7 15 " | 0.0249 | 22.4 8 " | 0.0498 | 23.9 4 " | 0.0898 | 21.6 40 seconds | 0.6156 | 24.8 25 seconds | 1.0998 | 27.5 8 " | 3.02813 | 24.2 4 " | 5.456 | 21.8 2 " | 8.453 | 16.9 1 " | 18.94 | 18.9 2/5 " | 45.05 | 18.0 2/25 " | 308.7 | 24.7 1/25 " | 511.4 | 20.5 1/55 " | 1255 | 22.8 1/100 " | 1902 | 19.0 1/400 " | 7905 | 19.8 1/800 " | 13094 | 16.4 1/1000 " | 26520 | 26.5 ---------------+--------------+---------- It is, therefore, obvious that the blind instinct which forces animals to go to the light, _e. g._, in the case of the moth, is identical with the instinct which makes a plant bend to the light and is a special case of the same law of Bunsen and Roscoe which also explains the photochemical effects in inanimate nature; or in other words, the will or tendency of an animal to move towards the light can be expressed in terms of the Bunsen-Roscoe law of photochemical reactions.