1758 AGRICULTURAL BOTANY, CHEMISTRY AND PHYSIOI<OGY OF PLANTS 



even have a yellow ground with green ribs. This last phenomenon was ob- 

 served for the first time 8 or 9 days after the experiment had begun on the 

 third, fourth and fifth leaves. vSmall drops of ferric chloride placed on the 

 yellow parts of the leaves immediateh' caused green spots to appear. As 

 the plant got older the coloration changed. The sixth leaf always had green 

 ribs and the seventh was wholly green; the variegations of the fifth tended 

 to become less sharply defined, but the third and fourth leaves remained 

 unchanged. 



When a few drops of phosphoric acid were added to the cultures con- 

 taining carbonates, a faint greenish colour appeared at the base of the leaves 

 after 3 or 4 days; and plants grown in pots with calcium carbonate 

 were injected with 0.25 cc of ferric chloride solution (0.03 j)er cent) which 

 produced a green coloration in the parts above the point of injection. In 

 all the experiments on variegation, not only maize was used but also sor- 

 ghum, barley, buckwhet^t and beans; the last two plants, however, did 

 not behave in the Same manner as the other three. 



A last set of experiments was carried out with the nutrient solutions 

 of Hellriegel, Prianichnikov and Crone in order to test Benecke's theory 

 of chlorosis which was fully confirmed. 



Conclusions. — When plants are grown in culture solutions contain- 

 ning free carbonates, the chlorosis produced is due to the alkalinity of the 

 carbonates, more especially of calcium carbonate. This alkalinity is not 

 however a direct cause of chlorosis, but acts indirectly by making the 

 iron inaccessible to the plant. Such effects may also occur imder natural 

 conditions if the food solution be physiologically alkaline. 



The property possessed by iron of forming almost insoluble salts with 

 phosphorus prevents iron assimilation from taking place in nutrient solu- 

 tions. 



Chlorosis may be caused by absence of sulphur as well as by absence 

 of iron. 



There are often essential difference between the results obtained in 

 sand and in water cultures. 



Iron is particularly interesting in its strictly localized assimilation by 

 plant tissues, as shown by the experiments on " isolated nutrition ". This 

 should prove a means of obtaining valuable material for the stud^' of pro- 

 blems connected with the internal structure of plants. 



1271 - Influence of Calcium and Magnesium Compounds on Plant Growth. — wyatt 



F. A., in Journal of Agricultural Research, Vol. VI, No. 16, pp. 589-619. Washington, D. C, 

 Julj' 17, 191 6. 



Experiments were planned with the idea of studying the effects of 

 calcium and magnesium upon plant growth when applied in different na- 

 tural and artificial forms. Studies were made to determine the amount 

 of calcium and magnesium which plants could tolerate. The relation be- 

 tween the ratio of these two elements in the pi ants, in the soils, and in the 

 materials .supplied was also studied. 



Dolomite, limestone, magnesite, calcaieous soils, and brown silt lo&m 

 were used as sources of the natural forms, while prej^ared materials , such 



