Nov. i8, 1918 Physiological Studies of Normal and Blighted Spinach 373 



as much as the roots in all samples. The proportion of silica present 

 seems to be little affected by health or disease either in tops or roots. 



It is interesting to note that in the analyses -reported by Wolff (49, 

 p. 141-150), the average silica content of this plant, presumably of the 

 tops, is but 4.52 per cent of the total ash against 28.15 per cent found 

 here, and but 0.745 per cent of the total dry weight of the plant against 

 5.78 per cent found in the normal Norfolk tops. It would be interesting 

 to know* in how far the silica content of spinach varies with the locality 

 in which it is produced. A high silica content seems in general to char- 

 acterize the grasses and grains and not such succulent vegetables as 

 spinach. .In this material, however, we have a quantity present equaling 

 that characteristic of the grains (49). 



In this connection it is interesting to note Bertrand's (5) conclusion 

 that the oxidase activity of plant tissues is related to the manganese 

 content. vSince the oxidase relations of normal and blighted spinach 

 are dealt with in a separate paper (p. 377), it is sufficient to state here 

 that in general the higher manganese ash content seems to accompany 

 the stronger oxidase reaction in agreement with Bertrand's observations. 



The tendency of calcium to become localized in the leaves in greater 

 quantity than in the roots is seen in both normal and blighted samples. 

 While .in the normal material the average proportion of the total ash 

 made up by calcium is about the same in tops and roots, in the diseased 

 plants the greater proportion is clearly found in the tops. When the 

 actual quantity of calcium present in a unit of dry weight is considered, 

 the tops are seen to carry more than three times as much as the roots in 

 both normal and blighted material and the diseased plants contain nearly 

 twice as much calcium as the corresponding structures of the normal 

 plants. There is here then a tendency of the diseased plants toward 

 increased accumulation of calcium in both tops and roots. It may be 

 noted in passing that according to the analyses given by Wolff (49, p. 

 141-150) spinach belongs among those plants which absorb calcium in 

 rather limited quantities, like many of the common legumes. This con- 

 clusion is confirmed by the results here given. 



Magnesium is present in both roots and tops of the blighted plants in 

 nearly double the proportion of the total seen in the corresponding parts 

 of normal plants and in both types of material forms a larger proportion, 

 of the ash of the roots than of the tops. 



When considered with reference to the actual quantity of magnesium 

 present in a given weight of dry material, that seen in the tops is about 

 the same whether diseased or normal, the quantity seen in normal roots 

 being less than that seen in roots of blighted plants. 



The magnesium content found here is roughly about one-half that 

 reported by Wolff (49), who lists spinach among the plants which absorb- 

 relatively large quantities of this substance. 



