458 Physiologie. 



With submerged plants, however, the case is different. 

 At 14 metres below the surface of the sea the active red rays 

 are wanting and the Hght is composed of green and blue, and 

 a small proportion of yellow, rays. At this depth the Rhodo- 

 phyceae are the dominant algae whose red pigment serves as 

 an efficient absorber of the green and blue rays, The Phaeo- 

 phyceae, which are found in shallower water in virtue of their 

 brown colour have an increased power of absorbing the green 

 and yellow light as compared with the green algae. That the 

 red algae do not dominate over the green at the surface is 

 probably connected with the fact that there the increased power 

 of absorbing light energy is of no assimilatory advantage. 



G a i d u k o V has recently shown that if Oscillaria be placed 

 in light of any given colour it will develope the complementary 

 colour in the cells of new growth. This change is not com- 

 pleted at once, but the successively formed cells exhibit a series 

 of chromatic changes culminating in the colour complementary 

 to that of the light in which the plant is growing. Gaidukov 

 gives the following series complementary to the spectral lights 

 in Order 1. Sky blue, 2. blue-green, 3, verdigris-green, 4. grey- 

 green, 5. whitish-grey, 6. violet to brown-violet, 7. brown, 8. 

 orange to reddish. In white light 0. sanda has colouration 6. 

 Placed in red light it passes up the series to 1. Placed in blue 

 light it passes through 7 to 8. In white light C caldarloviim 

 has cofour 2. Transferred to green light it passes down the 

 series to 7 or 8. 



Each new cell formed may only take a small step in colour- 

 change, and the plant goes on slowly in the direction of its 

 final tint. 



If brought back into white diffuse light the cultures retained 

 for months the colours acquired behind the coloured screens. 

 In this connection it should be noticed that white day light 

 probably supplies sufficient of all the rays to allow any of the 

 Oscillaria colours to assimilate abundantly, and hence there 

 would be no assimilatory gain in reversion of the cells to their 

 ancestral colour. E. Drabble (London). 



Darwin, F. and D. F. M. Pertz, Notes on the Statoüth 

 Theory of Geotropism. I. Experiments on the 

 Effects of Centripetal Force. II. The Behaviour 

 of Tertiary Roots. (Proc. Royal Soc. London. June 22, 

 1904.) 



Seedlings of Sorghum and Setaria react to a centrifugal 

 force of from 0,02 to 0,04 g. When the plants were placed 

 radially with their apices directed outwardly and were rotated 

 on a klinostat with horizontal axis there was manifested a slight 

 tendency for the starch grains to accumulate by radial move- 

 ment in the apices of the cells. By placing some seedlings 

 with their apices pointing outwards and others with apices 

 directed inwards it was shown that the starch-grains move 



