1893.] Mr. G. J. Komanee. Experiments in Heliotropism. 333 



8. The theory is applied to Professor Weldon's measurements on 

 Naples crabs. It is shown that his material is absolutely homo- 

 geneous, all roots of the nonic for No. 4 organ leading to imaginary 

 .solutions, even its real root. On the other hand, it is shown that 

 the Naples crabs are breaking up into two different sized families, 

 owing to evolution in their foreheads. The theory is farther 

 applied to Mr. Thompson's measurements of the carapace of prawns 

 (1,000 measurements). It is shown that we have in the measure- 

 ments a very small percentage of anomalous results, corresponding to 

 prawns deformed in this organ, or that there is, on the other hand, 

 a small but unstable giant population mixed with the normal popula- 

 tion. Which of these results is to be considered the true answer to 

 the problem can only be determined after an analysis of the frequency 

 curves for other organs. 



From the mathematical standpoint, the memoir illustrates the de- 

 termination of the roots of equations of the ninth degree, and the 

 -calculation of the higher moments of curves. 



IV. "Experiments in Heliotropism." By G. J. ROMANES, F.R.S. 

 Received October 2, 1893. 



I cannot find in the literature of heliotropism that any experiments 

 have hitherto been made on the effects of interrupted illumination, 

 when the periods of illumination are rendered as brief as possible 

 -i.e., instantaneous flashes of light. Accordingly I have conducted 

 an extensive research on heliotropism, where the flashes have been 

 caused either by means of electric sparks in a dark room, or by the 

 opening of a photographic shutter placed before the plants in a camera 

 obscura with an arc light or Swan burner, at a distance of several 

 feet on the other side of the shutter. The electric sparks were made 

 either with a Wimshurst machine, induction sparks, or by means of 

 the following contrivance. From the binding screws of the condenser 

 of a large induction coil copper wires were led to a cup of mercury, 

 where, by means of an electro-magnet suitably actuated by clock 

 work, a current was closed and opened at any desired intervals : each 

 break was therefore accompanied by a brilliant spark. A thick plate 

 of glass was interposed between the seedlings and the electrical 

 apparatus. In all the experiments here described the plants em- 

 ployed were mustard seedlings (Sinapis nigra), previously grown in 

 the dark until they had reached a height of between 1 and 2 inches. 

 Save when the contrary is stated, in all the experiments comparative 

 estimates were formed by using the same pot of seedlings : during 

 the first half of a comparative experiment half of the seedlings were 

 protected from the light by a cap of cardboard covering half the pot ; 



2 A 2 



