GLASS STKUCTURES AND APPLIANCES. 



325 



time after June prove tolerably efficient for this pur- 

 pose. It is a good plan to move some of the surface 

 soil before applying the mulch, as the pupae are likely 

 to be removed with it. Mulchings of spent tan, and 

 cinder-ashes, have also been effectual in shutting in 

 the pupae for good. Strong doses of sewage or other 

 manure water, and the careful clearing away of 

 all old dry soil around the boles, have also mode- 

 rated or wholly remedied the plague of caterpillars. 

 Another mode of destruction consists in picking 

 them off. Most of them are sufficiently large to be 

 seen, and should be looked for and destroyed. A good 

 plan also is to place two small sheets round the 

 trees so as to meet in the middle, then give the trees 

 a smart and sudden shake, which results in placing 

 many of the caterpillars on the sheet, when they may 

 be gathered up and destroyed. 



"Weevils. — There are many varieties of these, 

 some of them boring into the fruit in the same way 

 as the Codling Moth and the Saw-fly, such as the 

 Pui'ple Apple Weevil, Rhynchites Bacchus. Another, 

 the Stem-boring Weevil, R. alliarice, deposits its eggs 

 in the stems — the grubs, when hatched, scooping out 

 the pith of the young shoots, and so destroying them. 

 The Apple-borer, which is not exactly a Weevil, con- 

 fines its operations chiefly to the collar of the tree, 

 which it often weakens and not unfrequently destroys. 

 Then there is what is termed by many, by way of pre- 

 eminent destructiveness, the Apple Weevil, Anthono- 

 mus pomorum. This beetle sleeps in the bark or on the 

 ground during winter months, comes forth in eai-ly 

 spring, and deposits a single egg in each flower-bud. 

 Early in April, the egg is hatched into a grub, which 

 feeds on the pistil and other organs of fructification. 

 So soon almost as it has destroyed the fair promise of 

 a crop, the gTub is transformed into a beetle, and 

 immediately begins to feed upon and devour leaves 

 and even shoots. As these fade and decay, it bur- 

 rows or hides itself for the winter, and emerges 

 in the spring, and resumes the cycle of destruction. 

 By noticing carefully the first withered bloom, the 

 grubs may often be seen and squashed at work on 

 the buds and blossoms, and if seriously injured, it 

 is better to gather these en masse, grubs and all, and 

 destroy them. Surface consolidation and mulchings, 

 as already described, will also destroy many more, 

 and only by persevering by such methods can these 

 and the other Weevils be destroyed. The Branch- 

 boring and Collar-piercing Weevils may likewise 

 often be killed in their lairs by a thrust of a small 

 wire, or smeared in with messy and sticky smears, 

 or even a patch of cement. The constant scarifica- 

 tion and annual removal of the surface soil for 

 Apple-trees would also bother the Weevils, while, 

 were the same soil charred into burnt earth for 



seed-sowing, potato -planting, and other purposes, 

 a speedy end would be made of many of the insect 

 pests, which work such sad havoc among our Apple- 

 trees. Still, when all is done that experience can 

 suggest to wage a successful war against disease and 

 insects among our Apple-trees and bushes, cleanh- 

 ness and good culture are our best allies, and pre- 

 vention our only perfect cure for both. 



GLASS STRUCTURES AND 

 APPLIANCES. 



VENTILATIO'N. 

 By William Colemax. 

 rnHE ventilation and heating of horticultural 

 X structures being so closely connected, the satis- 

 factory working of one depending so much upon the 

 other, the preceding chapter on heading cannot be 

 considered complete without a few remarks on, and 

 diagrams illustrative of, ventilation. If we apply 

 artificial heat to a Vinery, no matter how efficiently, 

 the hot- water pipes do not radiate their heat pro- 

 perly without a circulation of air. If we ventilate a 

 Pine and plant stove, we can lower the temperature 

 by letting out at the top the heated or vitiated air, 

 and by the introduction of a cold current near or 

 below the ground-line ; but this is not scientific ven- 

 tilation. It is a system that may answer in what 

 are termed "cold" houses, or for hot-houses when 

 the external summer temperature is equal, or nearly 

 so, to that of the interior. But at other times, when 

 the discrepancy is very great, other means must be 

 provided for warming these cold currents before they 

 come in contact with the tender foliage of the plants ; 

 and here, in this particular case, heating and venti- 

 lating are so closely dovetailed together as to render 

 it simply impossible to carry out the one without the 

 aid of the other. All ventilation rests upon the 

 ^mple principle that cold air is heaxier and has a 

 tendency to descend, while warm air is light and rises 

 to the top. But how the air is to be wai-med and 

 made to take any particular course through a glass 

 structure, the roof of which is exposed to intense 

 solar Jieat, or the reverse, is a question which has 

 long occupied the minds of scientific and practical 

 men. For a long time neaiiy all that was thought 

 of was a system to prevent the atmosphere of the 

 structure from becoming over-heated, and this was 

 accomplished by making openings at the base and 

 apex, but this created draughts, which are always 

 objectionable. The late far-seeing Dr. Lindley 

 justly said: "The importance of aeration^'' (he 

 discards the term ventilation) " cannot be over-esti- 

 mated. It is the one thing which now requires to 



