222 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
and prevented the escape of the larvae. Now chitin, the substance 
of which the egg-shell consists, is a very resistant body, being quite 
unaffected by treatment with as strong an alkali as 10 per cent, caustic 
soda for a considerable period. It did not appear likely, therefore, 
that so weak an alkali as lime would have any appreciable effect. It 
was also found that the thicker the coat and the later it was applied 
the more effective it was. These facts clearly pointed to the sealing- 
in explanation as the correct one. In order to try to settle this 
point, twigs on which the eggs of apple-suckers were laid were brought 
into the laboratory and treated with various lime mixtures. Among 
these were lime wash in proportion of i lb. of lime to i gallon of water, 
2 lb. to i gallon of water — the latter being applied both freshly slaked 
and in the cold well slaked condition- — and a whiting-glue mixture, 
which gave a particularly firm coat. 
When the eggs on the control twig hatched, the results on the 
coated twigs were noted. It was found that on the one coated with 
the thinner lime wash, a considerable number of suckers had reached 
the buds. On both the twigs coated with the thicker lime mixture 
only very few were found in the buds, while the whiting-glue mixture 
had prevented the hatching of all but two. If now the action had 
been due to the causticity of the lime, one would not have expected 
many to hatch on the twig coated with the weaker but hot lime 
mixture, while one would have expected them to hatch in abundance 
on the twig treated with the thicker but well slaked and presumably 
non-caustic lime. 
The contrary was, however, the case. 
To make certain of what had happened the cover coat was in each 
case carefully dissolved off by dilute acid. It was then found that 
the apple-sucker eggs under the thicker coats had tried to hatch, 
nearly every egg being split. The dead larvae were found in all 
stages, some outside the egg under the lime coat, some half-way out, 
and some still inside. Anyone seeing these results could have no 
doubt that the action of lime was a mechanical one. 
If then the action is for the most part at any rate mechanical, 
it is most important to obtain the firmest and most resisting coat 
possible. The thickness of the coat at the time of hatching of the 
eggs will obviously depend on two factors : 
(1) The nature of the coat. 
(2) The time of its application. 
A very short experience of lime-spraying is enough to show that 
an ordinary lime coat leaves much to be desired. It is liable to flake 
and does not resist rain and wind well. 
In the winter of 1912-13 experiments were begun at Long Ashton 
in order to find some more effective coat than the ordinary lime spray. 
A large number of mixtures were tried, * and after two years a fairly 
* Lees, " Winter Cover Washes, " Ann t App._ Biol._ vol. i. nos, 3 and 4, and 
vol. ii. no. 4. 
