516 SUMMARY OF CURRENT RESEARCHES RELATING TO 



explains the stimulus to geotropic movement as caused by the falling of 

 the starch-grains on the cell-walls when an organ is moved from its 

 normal position in relation to gravity. The author, wishing to ; supple- 

 ment the evidence supplied by Haberlandt and Nemec, devised an 

 ingenious but simple method of experiment. If gravitational sensi- 

 tiveness is a form of contact-irritability (which must be the case if the 

 pressure of the statoliths on the plasmic membrane is the critical event) 

 then it might be possible to intensify the stimulus by vibration. By 

 applying vibration in a vertical plane to a horizontal seedling, the 

 repeated blows of the starch-grains on the protoplasm should produce a 

 more active geotropic response. This was realised by a tuning-fork ; 

 seedlings which had been kept horizontal for from 8 to 10 minutes on 

 a tuning-fork vibrating in a vertical plane showed about 44 per cent, 

 more curvature than the control specimen. The experiment was re- 

 peated with vertical specimens exposed to lateral illumination to make 

 sure that the enhanced response was not due to an increase in the 

 general irritability of the seedlings. In this case the curvature of the 

 vibrated plants was only 5 per cent, more than that of control speci- 

 mens. We may therefore conclude that vibration increases the geotropic 

 reaction but does not materially affect heliotropism ; which is what we 

 should expect on the assumption of the truth of the statolith theory. 



Chemical Changes. 



Hydrogen and Carburetted Hydrogen formed by Plants.* — G-. 

 Pollacci in a preliminary note describes briefly the experiments he has 

 made, and the apparatus he employed to demonstrate the emission of 

 free hydrogen and carburetted hydrogen by green plants during assimi- 

 lation in sunlight, The evolution of nascent hydrogen he believes to 

 be a potent factor in the formation of formic alhedyde in the assimilating 

 tissues. 



Experiments with Potatoes.! — E. Breal finds that when potatoes 

 are kept through the winter C0 2 and NH 3 are liberated. Chloroform 

 vapour checks the liberation of C0 2 , and when the action is prolonged 

 the tuber dies and a nitrogenous liquid is produced. Exposure to cold 

 retards the respiration of the tubers and causes the accumulation of a 

 reducing sugar. The organic nitrogen of potatoes is present partly in 

 an insoluble form and partly as albumin, which coagulates at 70°, and 

 partly as solanine. The tubers contain both nitric acid and ammonia ; 

 the former disappears when an ammonium salt is introduced. The 

 tubers produce snoots spontaneously in the spring, but require water to 

 form roots. The separated shoots can be made to grow when supplied 

 with suitable mineral food and potassium humate. Boots living in 

 water absorb ammonium salts, but only in absence of nitrates. 



Prussic Acid in opening Buds of Prunus.| — E. Verschaffelt finds 

 in Primus P cuius and P. Laurocerasus a steadily increasing absolute 

 quantity of HCN-compounds in the shoots growing from the opening 



* Atti d. Istit. Bot. Univ. Pavia, vii. (1902) pp. 97-100. 



t Ann. Agron., xxviii. (1902) pp. 545-76. See also Journ. Chem. Soc, lxxxiv. 

 (1903) ii. p. 175. % Proc. k. Akad. Wetensch. Amsterdam, v. (1902) pp. 31-41. 



