General Remarks. 581 



wire- worms, and grubs, is to hunt them out and kill them 

 outright ; but lice and caterpillars and other parasitical insects 

 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 

 larvae 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 nourishing in 

 a cold cloudy season. There is, moreover, a great difference in 

 the predisposition of different varieties of the same species (e.g. 

 Eoses) 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 

 in a 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 



