2l6 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
of the spray-fluid to be employed. It is of little use, for instance, 
treating an aphis attack by the application of lead arsenate, since 
this insect feeds, not on the leaf, but in it, so that stomach poisons 
on the surface of the leaf fail to act. 
Having thus discussed the conditions for successful spraying, 
the spray-fluids- themselves may be considered in rather more 
detail. 
In order to avoid confusion of treatment in this rather diffuse 
subject, it is well, if possible, to introduce some kind of classification. 
While I have never seen any definite system set forth by any writer 
on spraying, there is or was a more or less definite inclination to divide 
the subject into winter and summer treatments. Winter spray- 
fluids may be divided into those meant purely for cleansing the tree 
and those that are supposed to have a definite lethal action on insects 
or insect eggs. Summer spray-fluids are divided into : 
(1) Contact washes. 
(2) Stomach poisons. 
Into this system the comparatively modern practice of lime- 
spraying against such pests as apple-sucker fits badly, and I propose 
to adopt a rather different method, which has merits from the point 
of view of convenience, though it does not pretend to be a natural 
classification. It has been remarked previously that the life-history of 
an insect is highly important, since a knowledge of it enables one to 
pick out that stage which is most vulnerable. This is true enough, 
but it is not the only essential. The condition of the host plant must 
also be .considered, since this has much to do with ultimate success 
in insect control. It is possible, and indeed often happens, that when 
an insect is in the most vulnerable stage the host plant is also most 
sensitive to damage or is in some other way unsuitable for spraying. 
Thus the host plant, the apple, is in flower at a stage in the life-history 
of the apple -sucker when its eggs have hatched and the larvae are 
still fairly young and vulnerable, but the tree cannot then be sprayed 
with most spray-fluids owing to the likelihood of damage. Or again, 
at the viviparous stage of the apple aphis the insect is very easy to 
kill if only one can reach it with the fluid, but this is then almost 
impossible owing to excessive leaf -curl. 
I propose, therefore, to make the basis of the classification a 
temporal one, and to divide spray fluids according to whether they 
are applied in : 
(1) The active season. 
(2) The semi-dormant season. 
(3) The dormant season. 
By the active season is meant the time when the tree is nearly or 
quite in full leaf, which thus extends from late spring till late autumn. 
The dormant season indicates that period when the buds are resting 
and there is no foliage present — that is, during the winter. Semi- 
dormant is a clumsy term, used for the want of a better. By it is 
meant that period from the time when the buds just begin to burst 
