SOIL CONDITIONS AFFECTING PLANT GRO WTH 87 



Table XXVII. — Effect of Soluble Salts on Germination. Guthrie 

 AND Helms (117). 



When a solution comes in contact with a seed it does not 

 necessarily enter as a whole. Adrian Brown (58) has shown 

 that the barley seed is surrounded by a membrane which has 

 the remarkable property of keeping out many dissolved sub- 

 stances and allowing the water only to pass in, so that the 

 solution loses water and becomes more concentrated. A 

 number of substances can, however, pass through the mem- 

 brane, and to these H. E. and E. F. Armstrong (5) have 

 applied the term Hormones. In general they have no great 

 affinity for water ; in the Armstrongs' nomenclature they are 

 anhydrophilic : they pass into the cell and there disturb the 

 normal course of events. Ammonia, toluene, ether, chloro- 

 form, are all highly effective hormones readily entering the 

 cells of seeds, leaves, etc., and hastening the normal sequence 

 of processes. 



Supposed Stimulation of Plants by Electricity, Heat, and 



Radium. 



The Electric Discharge. — It has often been stated that an 

 electric discharge increases the rate of growth of plants either 

 by direct action on the plant, or by indirect action in the soil. 

 As far back as 1783 the Abbe Bertholon (34) constructed his 

 electro-v^getometre, 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 



