146 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY, 



Infection by certain Fungi, the Relation of Temperature and Humidity to. 



By J. I. Lauritzen (Phytopathology, ix. pp. 7-35, Jan. 1919)- — The author 

 found degree of infection to depend largely upon the temperature and to 

 increase rapidly up to a certain point in several plants. The humidity per- 

 mitting infection varied generally between 92 and 100 per cent., but it was 

 found unnecessary that a film of water should be present over the leaf surface. 

 A bibliography is given. — F. J. C. 



Influence of Trees and Crops on Injury by White Grubs, The. By Stephen A. 

 Forbes (U.S.A. Exp. Stn. III., Bull. 187, Feb. 19 16). — Experiments show that 

 more eggs were laid in pastures than in any other crop ; small grain came next ; 

 fallow land, grown up of weeds, largely grasses, third ; clover and corn fourth ; 

 and meadow crops — excluding clover — were least sought by the egg laying 

 beetles. — V. G. J. 



Insect Eggs, Toxicity of Organic Compounds to. By W. Moore and S. 

 Graham (Jour. Agr. Res. xii. pp. 579-587, March 1918). — Compounds with 

 high boiling-point and slight volatility are more effective for dipping and 

 spraying insects' eggs than are those of low boiling-point and high volatility. 

 Compounds with low boiling-points kill freshly-laid eggs most readily, but 

 those with high are more toxic to eggs containing forward embryos. Paraffin, 

 both of high and low boiling-point, is destructive to old and young eggs. The 

 toxicity of vapour of organic compounds to insect eggs increases with the 

 increase of boiling-point and decrease of volatility. — F. J. C. 



Insecticide, A Promising New Contact. ByWm. Moore (Jour. Econ. Entom. 

 vol. xi. June 1918, pp. 341-342). — Nicotine oleate may be made directly from any 

 nicotine preparation containing free nicotine. Two and a half parts of a 40 per 

 cent, nicotine solution unites with one and three quarters parts of commercial 

 oleic acid or red oil. Four and one-fourth parts of this soap will then contain 

 one part of nicotine. Nicotine oleate, it is said, will cost the farmer about one 

 dollar per 100 gallons. 



Nicotine oleate diluted to give one part nicotine in 1,500 parts of water is 

 efficient against aphides. The oleate may be used to make an oil emulsion 

 spray. Ten parts of kerosine mixed with one and one-quarter part of com- 

 mercial oleic acid, adding two and one half parts of 40 per cent, nicotine sulphate 

 well shaken up, forms an emulsion ; which is again stirred with ten parts of water. 

 Diluted with 480 parts of water is useful against mealy bugs, white fly, and soft 

 scale. Emulsified with a heavy oil nicotine oleate should be valuable for the 

 destruction of scale insects and eggs on dormant trees. It is important to note 

 that soft water (rain or distilled) is essential with N. oleate. — G. W. G. 



Insecticides, Physical Properties governing the Efficacy of Contact. By W. Moore 

 and S. A. Graham (Jour. Agr. Res. xiii. June 10, 1918 ; pp. 523-538 ; 1 fig.). — 

 These authors continue their observations on Spray Fluids, particularly explaining 

 the difference between " wetting " and " spreading " of contact washes. There 

 must be wetting before there can be spreading, but it does not follow that where 

 there is wetting there must be spreading. 



Contact washes may be divided into two classes — (1) those which wet the 

 insect and are able to spread over its body surface and pass up the tracheae 

 by capillarity ; and (2) those which wet the insect and are able neither to 

 spread over the surface nor to gain entrance into the tracheae. 



Oil emulsions may enter the tracheae as such, or the oil remains after the 

 emulsion is broken down, and may spread over the insect and enter the spiracles. 



Tables show penetration of various chemicals, stained with Trypan blue, 

 into insect's tracheae. — G. F. W. 



Insecticides, The Mode of Action of Contact, Observations on. By William 

 Moore (Jour. Econ. Entom. vol. xi. December 191 8, pp. 443-446). — This paper is a 

 continuation of a paper on the physical properties governing the efficacy of 

 contact insecticides, and gives an account of some highly interesting experiments 

 proving that fat solvents, oils, and soaps are able to penetrate the tracheae of 

 insects by capillarity and may result in the death of the insect by their purely 

 mechanical action alone. It is necessary for this result to cover all or nearly 

 all of the spiracles. The inferences drawn are that for insects such as plant 

 lice, an insecticide killing in a mechanical way will give good results, but for 

 larger insects it is necessary to add to the wash an insecticide capable of killing 

 in a chemical manner to insure death, as it becomes unlikely that all the tracheae 

 would be blocked. It is interesting to note in passing that the efficacy of free 

 nicotine sprays has been increased 50 per cent, by the addition of soap. It was 



