ANNUAL REPORT, 1947-48 9 



The Relationship of Plant Development to the Capacity to Utilize Potassium 

 of Orthoclase Feldspar. (Walter S. Eisenmenger and Cornelius C. Lewis.) 

 Twenty-two seed plants of varying degrees of development were grown in soil 

 in three series. To one series no potassium was added; to another, potassium 

 chloride; to the third, feldspar in quantity equivalent in potassium content to 

 the second series. At maturity the potassium content of the plants was de- 

 termined by chemical analysis, and percentage gains in all series were computed. 



The percentage gain of potassium from both soluble and insoluble sources 

 tended to decrease as the plants ascend from the lower to the higher order of 

 development. 



In the control medium, plants of the lower orders showed deficiency symptoms 

 earlier than those of the higher orders. 



The lower developed plants, such as larkspur, rape, poppy, lespedeza, velvet 

 leaf, and geranium, absorbed a larger quantity of potassium from the orthoclase 

 feldspar than did the more highly developed plants such as lettuce, sunflowers, 

 sage, and spinach. With few exceptions, the lower the plant in its development, 

 the more easily it secured potassium from relatively insoluble sources. 



Magnesium Requirements of Certain Plants. (Walter S. Eisenmenger and 

 Karol J. Kucinski.) The need of plants for magnesium to maintain normal 

 physiological processes is not easily determined because the amounts of the ele- 

 ment required by different species are not the same. The magnesium require- 

 ment is higher for garden crops than for such crops as wheat, rye, or oats. Some 

 of the hybrid varieties of corn are seemingly unable to secure sufficient magnesium 

 from magnesium-deficient soils where open-pollinated corn may grow normally. 

 With the exception of a few botanical families, the more highly developed plants 

 do not show magnesium deficiency symptoms to the same degree as do the 

 lower orders of plants. This may mean either that the lower orders of seed plants 

 need more magnesium or that they are more sensitive to abnormal conditions. 



The pH of a soil influences the degree of magnesium deficiency. On a soil 

 which was magnesium-deficient and which had a pH of 6.8, there was less chloro- 

 sis and growth was less retarded than on a magnesium-deficient soil where the 

 pH was 4.5. This is probably due to the more rapid washing out of the magnesium 

 ions from the weathering rock particles under lower pH conditions. Magnesium- 

 deficiency symptoms are not usually present where the soil has a high pH value 

 or high organic mattar content. It has been observed that magnesium deficiency 

 in plants is associated with soils having a low base exchange capacit}'. 



When magnesium salts are applied to a soil where annuals are grown, an in- 

 crease in the magnesium content of the plant tissue is found. This is not true 

 for all perennials. Certain species of perennials, as they grow older, seem to lose 

 their capacity to increase their magnesium content. 



Magnesium Deficiency Investigations. (W. S. Eisenmenger and Dale A. 

 Hinkle.) Analyses of leaves from 18 diff^erent species of plants which were grown 

 on magnesium-deficient and magnesium-treated plots showed that a deficiency 

 of magnesium in the soil greatly reduced not only the chlorophyll content of 

 leaves but also the xanthophyll and carotene content. Coefficients of correlation 

 between the losses of any two of the three pigments were high and positive. 

 When the chlorophyll content was used as a criterion of magnesium deficiency, 

 it appeared that, for the most part, those plants low in the scale of evolutionary 

 development suffered more from magnesium deficiency than plants higher up in 

 the scale. 



