50 SOIL CONDITIONS AND PLANT GROWTH 



on the plant, or by indirect action in the soil. As far back as 1783 

 the Abb6 Bertholon (34) constructed his electro-v^g^tometre, a kind of 

 lightning conductor that collected atmospheric electricity and then 

 discharged it from a series of points over the plant. The view that 

 atmospheric electricity is an important factor in crop growth has always 

 found supporters in France. Grandeau (112) stated that plants pro- 

 tected from atmospheric electricity by a wire cage made less growth 

 than control plants outside. 



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 recently been 

 much developed at Bitton, near Bristol, on the electrical side by 

 Sir Oliver Lodge, on the botanical side by J. H. Priestley, and on the 

 practical side by J. E. Newman. 



In J. H. Priestley's experiments (230) the rate of respiration of the 

 plant was much increased under the influence of the discharge provided 

 ozone was not formed in appreciable quantity. The amount of tran- 

 spiration increased so that more water was needed, there was also a 

 marked acceleration in the ripening of the crop. The following crop 

 increases are said to have been obtained : — 



Wheat, 29 per cent. Strawberries, 25 per cent. 



Carrots, 50 per cent. Beets, 33 per cent. 



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) 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. 



