58 Journal of Agricultural Research vol. xx, No. 1 



surrounding the calcareous particles and those surrounding the other soil 

 particles. With moisture contents above the optimum the moisture 

 films become more continuous and the sphere of influence of the particles 

 of carbonate of lime in reducing the availability of iron becomes- more 

 extended. 



Incidentally the tests established a fact of considerable practical im- 

 portance — namely, that rice may be expected to make a practically 

 normal growth in certain calcareous soils if the soils are submerged. 



SUMMARY 



There are a few plants which are generally conceded to be calcifugous, 

 inasmuch as they are rarely found on calcareous soils. 



Soil surveys of several species of cultivated plants show that a parti- 

 cular type of chlorosis affecting these plants occurs only on calcareous 

 soils. All calcareous soils, however, do not induce chlorosis in these 

 plants. 



Addition of carbonate of lime to soils producing normal, calcifugous 

 plants causes the soils to produce chlorotic plants. 



It is, therefore, evident that a chlorosis of some plants is caused by, 

 or is associated with, the presence of carbonate of lime in the soil. 



The weight of the evidence from ash analyses of chlorotic plants seems 

 to point to a deficiency of iron in the ash as being one cause of the chlorosis, 

 with possibly an excess of lime as a contributory cause. 



Treatment of chlorotic plants with iron shows that a lack of iron in 

 the plant is at least one of the causes of lime-induced chlorosis. 



There is no evidence of a general "lime effect" in inducing chlorosis, 

 the different lime compounds affecting the plants differently. 



Rice, one of the plants sensitive to lime, does not appear to be sensitive 

 to the alkalinity of carbonate of lime except as this alkalinity influences 

 the availability of the iron. 



Lime-induced chlorosis seems to be due simply to a depression in the 

 availability of iron in calcareous soils. 



A number of pure organic iron compounds and concentrated organic 

 preparations proved to be inefficient sources of iron for rice in calcareous 

 soils. Bulky organic compounds such as stable manure, velvet bean 

 plants, and tobacco stems, when used in considerable quantity, however, 

 enabled the plant to secure more iron. 



The availability of iron in calcareous soils appears to be slightly 

 greater near the optimum water content of the soil than at higher per- 

 centages of water. 



Although rice becomes chlorotic in calcareous soils with ordinary 

 percentages of water, it will grow normally in certain calcareous soils 

 if the soil is submerged. This is believed to be due to the growth, under 

 submerged conditions, of a new kind of root that is better able to assimi- 

 late iron than the root formed in the soil with less water. 



