DISEASES OF PLANTS. 853 



ody for this suggi^sts itself, namely, the invparatiuii of the fields so that there 

 will not be a superabundance of moisture. 



The damping off occurs generally in the seed bed and is accompanied by a 

 superabumhince of moisture. This can be avoided by ditching alxnit tl'e seed 

 beds and tlie removal of some of tlie jtlants if they are growing too tliickly, 



The hollow stem disease is said to be a result of too vigorous nitrogen feed- 

 ing in the seed bed, the plants being extra forced. 



The root knot described is caused by nematodes and is i)revented l)y the 

 rotation of cro])s. As the nematodes affect a number of other plants, these 

 should be avoided in any system of rotation. 



The insects described are the fruit worm (Hcliothifi anniovr), cutworms, 

 and the white mold due to Pln/toptus <-(il(icl(i(I(>i)hora. This mite is said to 

 attack the tomatoes to such an extent at times as to produce on the stems a 

 white moldy ajipcarance. Sulphur spray, dry suli)bur, lime-sulpluu- spray, 

 and dry sulphur and lime are excellent remedies for its control. 



Diseases of tobacco in Dumbara, Z\ I'etch (Circs, and Ar/r. Jour. Itoij. Jint. 

 ildrd. Ccjilnii. ', (/.'^07), A o. 7, pp. 'iJ-ffS). — Brief descriptions an? given of a 

 number of diseases of tobacco, among them a root disease due to Fusarium ; 

 two leaf diseases, one of which is caused ))y a fungus tliat lias been recently 

 determined as C'crcospora nicotiana'; a disease called ash, which is said to 

 be one of the worst diseases in Ceylon, and is due to the Oi'dium stage of some 

 mildew, and the mosaic disease. 



Prevention of apple crown-g'all and hairy-root, G. (J. IIeugcock [Nat. Nur- 

 scryiiKiii, Jo ( t'.IOl). Xo. 7, ///;. 1D2, 19.3). — An account is given of the crown-gall 

 and hairy-root, the forms occurring on the apple being particularly described. 

 The author claims that crown-gall is of two forms, the hard crown-gall, which is 

 not contagious, and a foi-m called soft crown-gall, Avhich is possibly contagions. 

 The hairy-root is not contagious, but it exists in a number of forms, which are 

 describetl. 



P'or the prevention of the apple crown-gall and hairy-root the author advises 

 improved nursery methods of propagation, which involve budding, the careful 

 selection of root grafts, better wrapping of grafts, selection of scions, earlier 

 planting, etc., and attention to improved conditions of soil. 



The author states that his exiieriment on the removal of crown-gall from trees 

 indicates that aliout one-half of the trees treated recovered from the disease. 

 No experiment for the removal of hairy-root has been concludeil. 



Apple-tree mildew {Jrmr. Bd. Ayr. [London], IJf {1901), No. 6, pp. 358-360, 

 fig. 1). — A description is given of the apple-tree mildew caused by Sphcci'otheca 

 mali, which has become troublesome in orchards in certain parts of England. 

 The ascigerous form of the fungus is said to be very rare and occurs too locally 

 to account for the universal distributicm of the mildew in the spring. It is 

 thought on this account that either the fungus retains its power of germination 

 throughout the; winter, or that there is some form of hibernating mycelium. 



As a rule the fungus checks the growth of the branches and distorts the leaves, 

 covering them with a dense white i)owder. 



Infection of the leaves takes place only when they are quite young, and it is 

 believed that by cutting out the infected rosettes of leaves and spraying the 

 trees with a solution of potassium sulphid the disease could be held in check. 



While there does not appear to be any definite proof that the fimgus is asso- 

 ciated with scale insects and green flies, yet it appears to be most abundant on 

 trees infecte<l by these pests. 



Cherry leaf scorch, E. S. Salmon (Jour. Bd. Ayr. [London], l) (1901), Xo. C. 

 pp. 334-3.'i'f, pi. 1, figs. 2). — A description is given of the disease kuowu as 



