88 SOIL CONDITIONS AND PLANT GROWTH 



supporters in France. Grandeau {\i2b) stated that plants 

 protected from atmospheric electricity by a wire cage made 

 less growth than control plants outside. Lesage ^ confirmed 

 this observation, but found that silk thread caused as much 

 retardation as wire, so that the effect is not necessarily 

 electrical : in point of fact the rate of evaporation was con- 

 siderably less under the cage than in the open. 



Instead of relying on atmospheric electricity Lemstrom 

 (171) generated electricity on a large scale and discharged it 

 from a series of points fixed on wires over the plant. This 

 method has been used at Bitton, near Bristol, and studied on 

 the electrical side by Sir Oliver Lodge, on the botanical side 

 by J. H. Priestley (231), and on the practical side by J. E. 

 Newman, J. H. Priestley, I. Jorgensen, and Miss Dudgeon. 

 Numerous field experiments are recorded, but there is usually 

 some uncertainty about the check plots. The Bromberg 

 experiments (104^) gave negative results. Further studies 

 are in hand by V. H. Black man who has put the whole 

 subject on a sound basis for investigation. 



Various Rays. — Experiments by Miss Dudgeon suggest 

 that the rays of the Cooper-Hewitt mercury vapour lamp^ may 

 have a stimulating effect, accelerating germination and in- 

 creasing growth. Priestley found that the rays from a quartz 

 mercury vapour lamp were harmful at close range, whilst 

 farther off they stimulated growth. There is much scope for 

 work in this direction ; the problem is of great economic 

 importance, because of the enhanced market value of early 

 crops. 



Effect of Heat. — Molisch^ has shown that perennial plants 

 steeped in hot water towards the close of their deepest 

 period of rest come at once into activity. His hypothesis is 

 that the "rest" required by plants is of two kinds, the 

 freiwillig rest due to external conditions and therefore cap- 

 able of being shortened, and the unfreiwillig rest inherent in 



1 Compt. Rend., 1913, 157, 784. ^ A glass envelope was used. 



'^Das Warmbad als Mittel zum Treiben der Pflanzen, 1909, Prague. 



