General Remarks. 5381 
wire-worms, and grubs, is to hunt them out and kill them 
outright ; but lice and caterpillars and other parasitical insecta 
may be kept under pretty well by syringing the plants attacked 
with tobacco-water, or a solution of some of the compounds 
manufactured for this purpose. Birds aid materially in dimi- 
nishing the number of these injurious insects. Wasps and ants, 
but notably the different species of Ladybird (Coccinella) con- 
sume myriads of the green fly. The Lime, amongst trees, is 
especially liable to the ravages of caterpillars, but nearly all 
deciduous trees and herbs are subject to the attacks of different 
species. In the case of large trees, it is usually left to the birds 
to destroy them; but much may be done to stay the ravages, 
particularly of those species infesting Conifers that deposit their 
larvze in large nests, by cutting off the small branches and burn- 
ing them. Amongst reptiles, lizards and toads may be con- 
sidered as the most useful, as they subsist entirely upon insects 
and slugs. And gold-fish not only add to the attractions of a 
lake or aquarium, but also serve to purify the stagnant water. 
The havoc and devastation caused by parasitical Fungi exceed 
that caused by all other injurious agents, and where they have 
once established themselves, there is greater difficulty in dispos- 
sessing them than is the case with insects. There are many 
species or varieties, or what are now known in some cases to be 
different stages or conditions of the same species, constituting 
what is popularly called Mildew. It is still doubtful whether 
these Fungi attack perfectly healthy plants, or whether they are 
the effect of bad health, the cause being attributed to unfavour- 
able conditions of temperature and soil, which produce decay of 
the epidermis and thereby expose the plant to the attacks of 
these parasites. However that may be, there are always accom- 
panying unhealthy symptoms, and mildew is most flourishing in 
a cold cloudy season. There is, moreover, a great difference in 
the predisposition of different varieties of the same species (e.g. 
Roses) to the attacks of these insidious organisms; some are 
subject to mildew almost every season, whilst others as rarely 
betray a trace of its presence, even though growing in the 
midst of infected plants. This much is certain, that plants 
_ ina healthy, vigorous condition will outgrow the disease much 
better than stunted, weakly ones will. But of course this does 
not materially aid in the elucidation of the first cause of the 
appearance of these parasites on different plants. 
Mildew in all its forms, if taken at an early stage, before it 
