Oct. i, 1920 Cause of Lime-Induced Chlorosis 47 



Summary. — None of the sprays affected the growth or color of the 

 plants, either in the normal soil or in the soil containing sodium bicar- 

 bonate. The amount of sodium bicarbonate required to depress growth 

 was rather surprising, and from this fact it was suspected that the availa- 

 bility of iron was not noticeably depressed by sodium bicarbonate, at 

 least not below the critical point. This was confirmed by the analyses 

 of the plants and by the fact that spraying with ferrous sulphate effected 

 ■no improvement in either the growth or color of the plants planted in 

 the soil containing sodium bicarbonate. 



The spraying with lime salts, however, notably increased the amount 

 of lime in the plants without affecting the quantity of iron, and spraying 

 with both lime and iron solutions increased the quantities of both ele- 

 ments in the plant. The yellowing and depression in growth produced 

 by the sodium bicarbonate were probably due to an injurious degree of 

 alkalinity, which must have been far greater than that which is produced 

 by carbonate of lime. 



The results of these experiments, where a large amount of sodium 

 bicarbonate was required to depress growth, seem to show that the slight 

 alkalinity of carbonate of lime could not be directly injurious to rice, 

 nor could alkalinity in itself be the cause of chlorosis. While this exper- 

 iment failed to yield the decisive answer expected, it is felt that the 

 results point strongly to the conclusion that an increased assimilation of 

 lime is not the cause of chlorosis. 



CHLOROSIS DUE SIMPLY TO A DEPRESSION IN AVAILABH.ITY OF IRON IN THE SOIL 



An attempt was made to demonstrate directly that the only action of 

 carbonate of lime in inducing chlorosis lies in depressing the availability 

 of the iron. It was thought that this demonstration could be accom- 

 plished by growing rice plants with their roots divided between two 

 kinds of soil, one to contain carbonate of lime and all the mineral nutri- 

 ents except iron, and the other to contain only iron. The attempt was 

 not completely successful, due partly to a principle discovered later and 

 partly to difficulties in execution. The principle which tended to make 

 the results less striking than had been anticipated is the following: 

 Plants apparently are unable to attain a maximum absorption of any 

 one element with only a part of their roots (18). 



Wire sieves were made which fitted into the tops of buckets. The 

 buckets were filled with soil to within 1 inch of the bottom of the 

 sieves, and the sieves were filled with about 2 inches of soil (PI. 5, B). 

 In this way an air space was left between the soil in the sieve and that in 

 the bucket; this prevented any soil solution passing by capillary attrac- 

 tion from the soil below to that above. It was the intention at first to 

 fill all except the control buckets with a calcareous soil containing all 

 the nitrogen, phosphoric acid, and potash, and to fill most sieves with 

 pure silica sand containing only iron. In conducting the experiment, 



