THE REQUIREMENTS OF PLANTS 51 



tected from atmospheric electricity by a wire cage made less growth 

 than control plants outside. Lesage (172) 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 considerably 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 (230), and on the 

 practical side by J. E. Newman. 



Numerous field experiments are recorded but there is some un- 

 certainty about the check plots, and further studies are in hand by 

 Priestley. The Bromberg experiments (103) gave negative results. 



Various Rays. Recent experiments of Miss Dudgeon are quoted 

 by Priestley to show that the rays of the Cooper-Hewitt mercury 

 vapour lamp have a very stimulating effect, accelerating germination 

 and increasing growth to a remarkable extent. Priestley found that 

 the rays from a quartz mercury vapour lamp were harmful at close 

 range, whilst farther off they stimulated growth. There is great 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 (203) 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 capable of being shortened, and the unfreiwillig rest in- 

 herent in the nature of the plant. Parkinson (225*2) has tested the 

 method with satisfactory results; spirea, rhubarb, seakale, etc., steeped 

 for twelve hours in water at 95, at the end of November, or early in 

 December, made rapid growth when subsequently forced. 



