LIMITS OF ENDURANCE OF DIFFERENT FARM CROPS. 191 



POT EXPERIMENTS TO DETERMINE the LIMITS OF 



ENDURANCE OF DIFFERENT FARM-OROPS FOR 



CERTAIN INJURIOUS SUBSTANCES. 



By F. B. Guthrie, f.i.c, f.c.s., and R. Helms. 



[Read before the Royal Society of N. S. Wales, October 8, 1902.'] 



Part I. — Wheat. 

 The following experiments were carried out in order to 

 test tlie effect upon the growth of the wheat-plant of a 

 few of the chemical substances occasionally present in the 

 soil and in manures, and which are known when present 

 in excessive quantities to seriously interfere with the 

 growth and development of the plant. 



The experiments were carried out in cylindrical culture 

 pots of galvanized iron, 8 inches high and 8 inches in 

 diameter. The pots were watered from below by means of 

 an external tube, communicating with a channel in the 

 bottom of the pot, a quantity of cinders and broken earthen- 

 ware being first introduced to ensure thorough aeration and 

 drainage. The pots were filled with the soil chosen for 

 the experiment, each pot containing about 18 flbs of the soil. 

 Through the kindness of Mr. Maiden, a space was set apart 

 in the Botanic Gardens in the open air, so arranged that a 

 tarpaulin could be at once unrolled to cover the whole 

 experiment in the event of heavy rain or wind. All the 

 pots were exposed to exactly the same conditions as to 

 light, warmth, water, etc., throughout the course of the 

 experiment. Check-pots were also filled, sown, and treated 

 in exactly the same way for purposes of comparison, omit- 

 ting the substances whose action was being studied. 



'Nature of the Soil. — Two kinds of soil were used. That 

 w r ith which the pots were originally filled, and in which 



