No. 3, January, 1922] PHYSIOLOGY 201 



MINERAL NUTRIENTS 



1335. DnGQAR, B. M. The use of "insoluble" salts in balanced solutions for seed plants. 

 Ann. Missouri Bot. Card. 7 : 307-327. 1920. — Results of experiments prepared "to determine the 

 possible value of certain relatively insoluble salts in furnishing the necessary ions for the 

 growth of seed plants" arc reported. If such salts should slowly become available in culture 

 solutions "it would only be necessarjf to add to the culture vessel a surplus of the substances 

 required" in order to imitate in some measure " the chemical relations in the soil." Thus as 

 the plants absorb certain ions the equilibrium of these ions might be maintained by the further 

 solution of the substances furnishing the ions. "As sources of Ca, Mg, Fe, PO*, SO4, many 

 insoluble salts have been tested, but no salt of this type is procurable as a practical source of 

 NO3, so that in most experiments this ion is furnished by KNO3. A relatively insoluble source 

 of NH4 (Mg NH4 PO4) has been found unsatisfactory as a source of nitrogen with the test plants 

 used. In each of three series of cultures in which wheat or wheat and corn were used, 

 one or more of the combinations containing two or more insoluble salts exceeded the growth 

 in the best control solution," which contained CaS04, MgS04, soluble ferric phospate, and 

 KNO3. "In all series, with the test plants mentioned, a group of cultures approached 

 very closely the yields of the best combinations, and in all cases in such best combinations 

 the calcium salt is relatively more soluble than the magnesium salt, except in certain combina- 

 tions into which ferric citrate enters. Soluble ferric phosphate has proved a valuable con- 

 stituent in the culture medium in a variety of combinations. In certain cases ferric citrate 

 has proved equally valuable." — S. M. Zeller. 



133G. GiLE, P. L., AND J. O. Carrbro. Assimilation of nitrogen, phosphorus and potas- 

 sium by corn when nutrient salts are confined to different roots. Jour. Agric. Res. 21 : 545-573. 

 1921. — The paper reports the results of an investigation concerning the assimilation of nitro- 

 gen, potassium, and phosphorus when either all the roots were contained in 1 culture vessel 

 with all nutrients, or when the roots were divided between 2 solutions each of which lacked 1 

 or 2 elements, or 1 solution was complete and the other lacked 1 or 2 elements, or when the roots 

 were divided among 3 flasks each of which lacked 1 or 2 elements. Corn, Zea il/ays, was used 

 in all the experiments. In all nutrient solutions except those lacking potassium the ratios of 

 bases were as follows: 1 Mg: 4 Ca : 5.3 Na : 14 K. In the solution lacking potassium the ratios 

 were 1 Mg: 4 Ca:6Na. Calcium carbonate was used in all cultures. For each treatment 16 

 plants were used. — The paper contains many detailed figures with respect to root growth, 

 growth of tops, percentage of total roots in the different culture vessels, analytical data on the 

 percentage of nitrogen and K2O in roots and N, K2O, and P2O5 in tops, as well as figures on 

 the mean assimilation of N, PaOs, and K2O relative to that of the control plants, all roots 

 of which were grown in flasks containing the complete solution. — Some of the general facts 

 brought out are as follows: Depression of growth and assimilation of nutrients are related to the 

 extent to which nutrients are restricted to separate root portions; ratio of root to top growth 

 increases with depression of total growth and assimilation of nutrients; growth of roots in the 

 complete nutrient solutions is "bushy" in habit and greater in extent; in solutions containing 

 nitrogen root growth was greatest. Withholding nitrogen from a part of the root system does 

 not manifest itself so strikingly in the nitrogen content of those roots as withholding either 

 phosphorus or potassium affects the content of these elements. — It is suggested that the dimin- 

 ished assimilation of nutrients under the conditions outlined is not due to inability of roots to 

 absorb the ions with sufficient rapidity, but is due rather to the slowness with which the ions 

 are translocated to the cells where they are utilized. When, for example, the roots arc divided 

 into 3 portions, each portion supplied with only 1 of the 3 elements, then, according to the 

 author, it is probable that each element is translocated in different bundles separated from 

 each other. The tissue adjacent to any group of bundles may have a surplus of the 1 element, 

 but the utilization of this 1 is dependent on the other 2, which reach this tissue only Avith diffi- 

 culty. — The increased ratio of roots to tops with decreased assimilation may be due to the fact 

 that the root growth is less influenced; or the greater relative root growth may be due to in- 

 creased movement of organic compounds to the roots, due to a reduced supply of nutrients 

 in the stalk and leaves. — Lewis Knudson. 



