Oct. i, i92o Cause of Lime-Induced Chlorosis 57 



early growth without submergence. Several of the surplus plants in the 

 pots with excess water were brushed repeatedly with ferrous sulphate, 

 but the treatment did not improve the color of the plants in the slightest. 

 Evidently this particular chlorosis is not due to lack of iron. Doubtless 

 when the water content of the soil is raised above the point of saturation 

 the old roots are unable to function properly and the nutrition of the 

 plant is disturbed until new roots are sent forth which are able to function 

 under the new conditions. 



It was thought that roots of the submerged plants might show morpho- 

 logical differences from roots of plants grown with ordinary amounts of 

 water in the soil. Samples of roots from plants grown in soil No. 1647 

 were therefore subjected to a preliminary examination by Dr. Albert 

 Mann, of the Bureau of Plant Industry, United States Department of 

 Agriculture, to whom thanks are due. A portion of Dr. Mann's report 

 of the preliminary examination follows: 



The differences noted between No. 1805 with 24.2 per cent moisture, 1807 with 

 32.2 per cent, and 1809 with water standing three inches above the surface are slight. 

 There is in general more compactness and strength of tissue in 1805 than in the others. 

 The central fibrovascular bundle mass is larger in proportion to the cortex than in 

 1807 or 1809. The cells of all the tissues are slightly more robust. The light paren- 

 chyma, which makes up the cortex from the endodermal ring to the epiderm, is es- 

 pecially thinner walled and more developed in 1809. There is also a notable absence 

 of root hairs in this sample as compared with the other two, which is, of course, the 

 inevitable result of the roots growing submerged in water. 



The series in the noncalcareous soil shows that the growth of rice 

 should increase regularly with increasing amounts of water in the soil 

 until a percentage near the saturation point of the soil is reached and 

 that, possibly because of a different root growth, there should be another 

 considerable increase when enough water is added for submergence. In 

 No. 1648, however, the series with the calcareous soil, there were two 

 maxima of growth, one at 24.2 per cent water and one at 3 inches excess; 

 and in the calcareous sand No. 1194 there were also two maxima. It is 

 believed that the first lower maximum was due to iron being a little 

 more available at that water content than at a higher content. The 

 great increase in growth in the calcareous soils produced by submergence ? 

 was probably due chiefly to the fact that the modified roots are better 

 able to assimilate iron than the ordinary type of root and was probably 

 not due to increased availability of iron in the submerged soil. 



It is felt that the results substantiate the idea that the availability of 

 iron in the soil is affected somewhat by the amount of water in the soil, 

 the availability being slightly greater near the optimum water content 

 than with larger amounts. 



The effect of the water content is probably due to its influence on 

 the extent to which reactions take place between the moisture films 



1 It will be noted that in the calcareous soils the increase produced by submergence was much greater 

 than in the noncalcareous soil. 



