16G 



CASSELL'S POPULAR GAPDEXIXG. 



air, as it were, twice, nay, many times, and far less 

 will he needed than if it has been longer delayed. 

 Not only this, but by delaying the giving of air, the 

 atmosphere is heated more rapidly than the leaves, the 

 latter and the fruit being dewed over in consequence. 

 Young cultivators look on this condensed aqueous 

 vapour with favour. It seems so soft, so fine, so 

 genial, and even enriching. Xo sooner, however, is 

 air admitted than away goes the aqueous vapour on 

 the wings of the dry air, and the leaves and fruit 

 get a severe check in consequence. 

 ■ The early giving of air so keeps down the tem- 

 perature that very little is needed ; and it may bo 

 remarked, that almost the less the better to tropical 

 plants in tropical houses, while there is considerable 

 disparity between the external air and the artificial 

 atmosphere in the houses. 



As the counterpart to the early opening of ventila- 

 tors, early closing should also be practised. By re- 

 moving all air, at, say, 4 p.m. or earlier or later, 

 according to the aspect of the house, an immense 

 amount of solar heat may be husbanded, almost 

 sufficient, often, to keep up the temperature through- 

 out the night, not only without injury, but with 

 positive benefit to the plants. By damping down 

 immediately, the hot air is filled with vapour, 

 and plants grow like willows throughout the night. 

 It may be remarked, in passing, that night is 

 the season of growth, and that if plants rest at all, 

 which they do not, it is in the day; the fact, how- 

 ever, being that they consolidate the growths made 

 in the night the next day, and elaborate and trans- 

 form the juices collected in the night into produce 

 by the help of the sun. But to return to our sub- 

 ject. The chief merit of most ventilation is motion^ 

 and it is astonishing how an interchange between 

 the external air and the internal atmospheres of hot- 

 houses insures perpetual motion. Ventilation is 

 also a useful means of controlling temperature ; but if 

 the heating apparatus is kept cool in the early morn- 

 ing of bright days, it is astonishing how slowly mere 

 sun-heat raises the temperature to injurious propor- 

 tions, especially in larger houses ; and, besides, ten, 

 fifteen, or even twenty degrees of sun-heat do far 

 less injury than ventilators thrown widely open to 

 keep it down. A very little air given, as the ther- 

 mometers begin to rise, will suffice as a sure and safe 

 regulator of temperature, and when air is not needed 

 for this purpose, none need be given, the hot air 

 within, and the cold air without, being sufficiently 

 intermixed without our aid, to maintain the purity 

 and freshness of our artificial tropics. 



Shading. — This is another means of husbanding 

 the resources of heat and moisture instead of reck- 

 lessly squandering them through open ventilators. 



Instead of setting these open and admitting a rush 

 of cold air to plant-stoves and Orchid-houses, let 

 down the blinds for an hour or two, and the proper 

 temperature is preserved. If air must be admitted 

 in tropical houses, let it in at the lowest point, and 

 make it pass over the hot-water pipes, and a part at 

 least of the open tanks, before its final dispersion over 

 and through the house. Treated thus, and warmed 

 and watered before distribution, it will do good and 

 not harm. 



Cleaning. — This is one of the most xitail among 

 every-day operations in tropical and temperate houses. 

 Cleanliness is the parent of health among jjlants 

 even more emphatically inside than out, and for this 

 reason, that the cleansing, natural forces of wind, 

 rain, and storm, are necessarily shut out from plants 

 under glass ; dust, soot, minerals in solution in 

 water, insect pests, the necessaiy operations of path 

 and stage cleaning, and labour — all tend to soil the 

 purity of plants. Hence, jets and showers of water, 

 the sponge, soft brush, <Scc., are, if not the breath of 

 life to them, at least means of enabling them to 

 breathe, absorb, and assimilate their food. 



This cleanliness is especially important among 

 Orchids, which, from their peculiar structure, afford 

 an infinitude of safe hiding-places for insects, and for 

 the storage of pollutions of aU kinds. 



Training Tropical Plants and Orchids. 



— Fortunately, the latter need little training, only 

 a few need much or any supports to the flowers, 

 and the long slender racemes of others look best 

 simply tacked up to prevent their getting bruised 

 or broken. Still, training and grouping are carried 

 to a gi-eat extent in the making up of Orchid 

 plants, that is, the forming of one or more specimens 

 out of a score or more plants, and so long as the 

 pilers up of beautj' in units into masses are satisfied, 

 no harm need be done. 



But other stove-plants as well as conservatory ones 

 need much training and caref ul staking and biinging 

 into shape. It is better at all times if they can be 

 grown into form, and kept in shape afterwaids, 

 without too. much training; but the limits to area, 

 and conveniences of easy portability, necessitate a 

 good deal of concentration and moulding of pot-plants 

 into handy forms by tying. 



The pruning and cutting back of plants when in a 

 semi-dormant state, and the stopping and pinching 

 of their shoots during the growing season, all come 

 under the heads of training. 



Potting or Shifting. — This constitutes the 

 larger and more important jDortion of the routine 

 management of glass-houses, and has already been 



