536 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Violet Leaf-spot. By M. D. (Irish Gard. xi. p. 5; Jan. 1916). — White spots, 

 round, with definite margins, occur on violet leaves, due to Phyllosticta Violae. 

 Recommends picking and burning foliage at the first onset of the disease, and 

 spraying with potassium sulphide. — F. J. C. 



Walnut Aphides in California. By W. M. Davidson (U.S. A. Dep. Agr., 

 Bull. 100, August 31, 1914)- — The life-history of walnut aphides in California is 

 briefly as follows : — A week or so before the buds open on the trees in the spring, 

 the aphides begin to hatch from the winter eggs. As soon as the young foliage 

 appears the " lice " settle on it, and after feeding for a month or so become 

 adults. These stem mothers are always winged, and, like plant lice of later genera- 

 tions, are capable of migrating to other trees and orchards. As soon as they 

 are fully developed they produce young parthenogenetically. These second- 

 generation young become mature in three weeks and in turn produce young. 

 The individuals of the third and subsequent generations of sumr.icr mature in 

 about sixteen days. 



In general the aphides inhabit the underside of the leaves, but those of the 

 second, third, and fourth generations often attack the nuts, sometimes seriously 

 dwarfing them. Occasionally the " lice " will be found on the upper surface 

 of the leaf. When infestation on the leaves and nuts is severe, the vitality of the 

 infested tree is impaired. The aphides excrete a sweet, gummy, transparent 

 substance much sought after by ants, and in this thrives a black, sooty fungus. 

 This black fungus often covers the upper sides of the lower leaves and the upper 

 part of the nuts, thereby interfering with the respiratory action of the plant 

 tissues. 



Aphides on walnuts can be controlled artificially with sprays. The winter 

 spraying directed against the eggs is the easier to apply, and high trees can be 

 reached by a winter wash with ease, whereas in the spring and summer so thick 

 is the foliage that a thorough application is hard to accomplish satisfactorily. 

 Furthermore, far less material is required when the trees are bare. Lime-sulphur 

 and crude-oil emulsions are effective, especially the first named. The spray should 

 be directed all over limbs and twigs, so as to cover every part. — A. D. W. 



Wetting, The Theory of, and the Determination of the Wetting Power of 

 Dipping and Spraying Fluids. By W. F. Cooper and W. H. Nuttall (Jour. Agr. 

 Set. vii. Part 2, pp. 218-239; Sept. 1915)- — The authors review the literature 

 of the subject and give an outline account of the physical principles involved. 

 They have conducted numerous experiments for comparing the wetting power 

 of a number of spraying and dipping fluids, and finally arrive at the conclusion 

 that the most useful method is that devised by Donnan (Zeitschrift f. Phys. 

 Chem. xxxi. pp. 42-49, 1899), which consists essentially in counting the number 

 of drops formed by a definite volume of a thick paraffin (the authors use liquid 

 vaseline) allowed to escape from a pipette dipping in succession into (a) distilled 

 water, (b) the spraying solutions under examination. The method is applicable 

 only to preparations containing soap as a basis. An interesting paper, whose 

 usefulness is increased by the appended references to previous literature. 



/. E. W. E. H. 



ERRATA AND CORRIGENDA. 



Page 30, line 3 from bottom, for Gnat moth read Goat moth. 

 „ 162 „ 5 ,, „ ,, £11 3s. read £1 13s. 

 ,,170 ,,9 ribicola read ribicolum. 



,, 205 ,,7 Mackii read Maackii. 



,, 206 ,, 30 for Strobilanthus read Strobilanthes. 



,, 13 from bottom, for Dalavayi read Delavayi. 

 376 3 for evert read erect. 



,,12 ,, \Thompsonianiim read Thomsonianum. 

 ,, xlv ,, 31 and 32 for C read N. 

 ,, xlvii ,, 15 for Coreus read Cereus. 

 ,, cxvi ,,37 ,, Taylor read Tayler. 



,, exxxii ,, 26 ,, Cydonia Mallardii read Pyrus japonica Wilsonii. 



