158 



Journal of Agricultural Research 



Vol. XXI, No. 3 



TABLE I. Effect of iron-sulphate spraying on mortality of western yellow pine seedlings 



a o.i pint of solution per square foot, equivalent to 0.02 inch of rain, applied to each treatment. 



The prevalence of chlorosis in the Pocatello Nursery during Septem- 

 ber, 1917, was determined by examining several thousand plants of the 

 different age classes of western yellow pine and Douglas fir. Of the first- 

 and second-year western yellow pine seedlings 82 and 62 per cent, re- 

 spectively, were chlorotic; while 74 per cent of the transplants grown 

 two years in the seed bed and one year in the transplant bed were 

 chlorotic. First-, second-, and third-year seedlings of Douglas fir were 

 chlorotic to the extent of 6, 65, and 26 per cent, respectively; while 15 

 and 62 per cent of the transplants grown three years in the seed bed 

 and one and two years, respectively, in the transplant bed were chlo- 

 rotic. 



OF WATERING 



It was at first thought that too heavy watering might have been 

 responsible for tihe chlorosis at the Pocatello Nursery. While an exam- 

 ination of the condition of the soil did not indicate water-logging, varia- 

 tions in the amount of artificial watering were tested. Four plots of 

 Douglas fir seedlings approximately 2 months old were given varying 

 amounts of water throughout a period of slightly over two months. 

 The results appear in Table II. The artificial watering was at first 

 given approximately once a week and amounted to the equivalent of 

 0.55 inch of rain on plot D, the most heavily watered plot. Plot C 

 received two-thirds of this amount, plot B one-third, and plot A none. 

 After the first month the amount of water added at each watering was 

 decreased because of the difficulty of avoiding run-off, and the frequency 

 of application was increased. The plots in this experiment were free 

 from chlorosis at the beginning of the period, and all of them later 

 exhibited more or less yellowing. The amount of water applied arti- 

 ficially, combined with the natural precipitation, did not total an ex- 



