DISEASES OF PLANTS 63 



dusting sulphur as a carrier, brought about good recovery of 

 affected plants so that new leaves were healthy and of a dark 

 green colour. No recovery resulted from similar treatment with 

 ferrous sulphate, which indeed had the effect of 'burning' the 

 leaves. 



Chemical analyses of normal, semi-chlorotic and chlorotic 

 leaves showed no very marked difference in the content of any 

 of the mineral constituents except manganese. The difference 

 in this element, however, between normal and affected leaves 

 is marked, the percentages of manganese in normal, semi- 

 chlorotic and chlorotic leaves being respectively 0-003, 0-0005 

 and a trace, 



The sand-culture experiments were carried out with cuttings 

 of a variety of sugar cane very susceptible to Pahala blight. 

 Manganese -free sand was used. Ten cultures were supplied with 

 a culture solution free from manganese while another ten, sup- 

 plied with a solution containing manganese, served as controls. 

 These latter plants grew normally, but the plants grown without 

 manganese gradually developed Pahala blight, and by the end 

 of six months the affection was quite severe. 



It may be noted that Lee and McHargue report that Pahala 

 blight only appears to occur on plants growing in alkaline or 

 neutral soils. Addition of substances such as sulphur and super- 

 phosphates which increase the hydrogen-ion concentration of 

 the soil and so make the manganese in the soil more readily 

 available for absorptionvwill tend to diminish the incidence of 

 Pahala blight. 



Speckled Yellows of Sugar Beet. The disease of sugar beet 

 known as speckled yellows also involves an intervenal chlorosis 

 in the leaves, the general appearance of the plant resulting from 

 the presence of the yellow chlorotic areas being indicated by its 

 name. As the disease progresses the margins of the affected 

 leaves curl upwards and over the upper surfaces of the leaves. 

 Other cultivated varieties of Beta maritima, namely, mangold, 

 red beet, and spinach beet, may also show the same condition, 

 although in red beet the characteristic speckled yellow effect 

 is masked by the red pigment present in the sap of the leaf 

 cells. Spinach (Spinacia oleracea), which belongs to the same 

 family as beet (Chenopodiaceae), may be similarly affected. 



