UPON ELECTRICAL STIMULI GENERALLY 43 



by J. H. Priestley, and on the practical side by J. E. Newman. 



" Numerous field experiments are recorded, but there is 

 usually some uncertainty about the check plots. The 

 Bromberg experiments gave negative results. 



" Various Rays. Recent experiments by 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 " 

 (too violent a discharge) " whilst further off they stimulated 

 growth. There is great scope for work in this direction ; 

 the problem is of great economic importance, because of the 

 enhanced value of early crops. 



" Effect of Heat. MoHsch 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 freiwilUg rest, due to external conditions and 

 therefore capable of being shortened, and the unfreiwillig 

 rest, inherent in the nature of the plant. Parkinson has 

 tested the method with satisfactory results ; spirea, rhu- 

 barb, 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." 



This I can quite understand as numerous experiments 

 have shown that the impetus to growth given by any 

 stimulus beneficial to the plant — or seed — continues for 

 some time after the stimulus has been cut off. 



" Effect of Radium. Among the many remarkable 

 properties of radium it was perhaps natural to expect that 

 it might have some definite effect on plants, and even, under 

 suitable conditions, cause sufficient increase in the amount 

 of growth to justify its use in horticulture and agriculture. 

 The early observations of Dixon and Wigham at Dublin, 

 however, did not seem very promising : one hundred seeds 

 of cress {Lepidium Sativum) were uniformly distributed 

 on an even surface of moist quartz sand, and after germina- 

 tion had taken place, a sealed tube containing five mgs. 



