360 



Lees (A. H.). Winter Cover Washes (Conclusion). — Ann. App. Biol., 

 London, ii, no. 4, April 1916, pp. 245-250, 2 tables. [Received 

 28tli July 1917.] 



During 1914-15, further experiments were made by the author to 

 find a mixture for winter cover- washes that could be made cheaply 

 and easily [see this Review, iii, p. 286]. Trials with starch, resin and 

 casein proved that they rendered the coating so soft that it was easily 

 washed off by the rain, and the same was the case when macerated 

 paper was incorporated as a binding substance. The cost of boiled 

 linseed oil rendered it unsuitable, though it might otherwise have 

 given good results. Mixtures of lime and glue proved failures owing 

 to the precipitation of the glue by the alkali, but further experiments 

 showed that cold well-slaked milk of lime added to a cold solution of 

 glue gave no such precipitate for several hours, but on the contrary 

 a firm thin coating. A mixture of 30 parts lime, 2 parts glue and 100 

 parts water gave a thick firm coat which weathered somewhat on 

 exposure to rain. The plan was tried of warming the lime so as 

 to cause the glue gradually to become insoluble as it dried on the tree, 

 but any delay, such as that due to choked nozzles, rendered the glue 

 insoluble before it reached the tree, thus lessening the covering power 

 of the mixture. The desired effect was however obtained by the 

 addition of potassium bichromate, which on exposure to light causes 

 glue to become insoluble. The best working formula therefore is : — 

 lime 30 lb., glue 2 lb., potassium bichromate | oz., water 10 gals. To 

 make it, 30 lb. of lime is put in a tub and 6 gals, of water poured 

 over it. When the lime begins to boil, 2 more gals, of water are 

 gradually added. Then 2 lb. glue is put into a pail with 1 gal. of 

 cold water and occasionally stirred. When the lime has slaked and 

 become cold (after about 6-12 hours) one gallon of hot water is added 

 to dissolve the glue and this is added to the lime, well stirred and 

 filtered through a 16 mesh to the inch sieve into the spraying machine, 

 and the potassium bichromate, previously dissolved in a little water, 

 is added and the whole stirred. The approximate cost of this mixture 

 works out at l^d. a gallon. 



Lees (A. H.). Some Observations on the Egg of PsyUa mali. — Ann. 

 App. Biol, London, ii, no. 4, April 1916, pp. 251-257, 8 figs. 

 [Received 28th July 1917.] 



It has been known for some years that the egg of Psylla mali (apple- 

 sucker) hatches at slightly different times on different varieties of 

 apple trees, the correspondence between the dates of bud bursting 

 and egg hatching being so close as to suggest some intimate relation 

 between the egg and the plant. Theobald has suggested that the heat 

 generated by the flow of sap to the opening buds regulated the hatch- 

 ing of the eggs. A microscopical examination of the eggs, which are 

 laid chiefly at the base of the fruit-spurs, reveals the fact that the two 

 outer membranes are produced at the posterior end into a hollow 

 process that is inserted in the bark. At first it was thought pos- 

 sible that the mouth-parts were contained in this process and that 

 there was a physiological connection between the egg and the tree ; 

 but this is not the case, the mouth-parts lying at the opposite end of 

 the egg. Another view, that the sudden increase of pressure of the 



