THE ORCHID WORLD. 



derived from the watering of the plants, and 

 the usual procedure of " damping down." 



The atmosphere always holds, in invisible 

 suspension, a varying quantity of moisture. 

 It is, in point of fact, never dry, or in any 

 way near dryness. Even when the air 

 seems parching hot, drying the skin and 

 withering vegetation, it is easy to demon- 

 strate by the aid of chemical agents the 

 existen:oe of moisture. 



The air has a wonderful power of absorb- 

 ing water, the amount held in suspension 

 being correlative with the degree of atmo- 

 spheric heat at the time. The higher the 

 temperature, the larger the amount of water 

 absorbed by the atmosphere ; when all its 

 interstices are full, it is then said to be at its 

 point of saturation, and any further supply 

 of moisture becomes visible in the form of 

 steam and moisture. 



This saturation point can be produced at 

 any temperature, for it only depends on there 

 being sufficient water to fill all the interstices 

 of the atmosphere. It is easily understood 

 that when the air is in a cold and, therefore, 

 condensed state there are few interstices to 

 fill, consequently very little water will be 

 required to produce this point of saturation. 

 A rise in the temperature expands the air, 

 with the result that more interstices are 

 formed and a corresponding amount of water 

 will be taken up. 



Therefore, whatever amount of moisture 

 has been absorbed by a certain degree of 

 temperature that amount will be lessened 

 proportionally with the cooling of the atmo- 

 sphere, and the result must necessarily be a 

 deposition of moisture, or, in other words, a 

 fall of dew. 



How does this law of Nature concern 

 the atmosphere of the Orchid house? The 

 temperature at the break of day is usually at 

 its lowest, but increases rapidly with the 

 advancement of the morning until, about 

 mid-day, it is at its highest. During this 

 period considerable absorption of the mois- 

 ture produced by damping down, and that 

 given off from the ground, has taken place, 

 the Orchids greatly enjoying this delight- 

 fully warm, moisture-laden atmosphere. 



7 



As the daylight fades so the atmosphere 

 becomes cooler and much of the suspended 

 moisture is condensed on the plants in the 

 form of dew. This dew is very beneftdal to 

 cool growing Odontoglossums, but somewhat 

 detrimental to plants, such as Cattleyas, in 

 flower. Hence we see that much success in 

 growing Orchids will depend on the correct 

 application of methods for controlling the 

 moisture m the atmosphere. 



In houses where a continuously moist atmo- 

 sphere is required, the temperature must be 

 maintained at night-time by artificial means, 

 or considerable deposits of moisture will be 

 formed to the detriment of the plant. 



In houses occupied by plants in flower, or 

 those requiring a drier atmosphere for pro- 

 ducing ripening of the bulbs in autumn, 

 a cooler night temperature is beneficial. 

 Therefore, to prevent drip and the formation 

 of dew, much of the atmospheric moisture 

 must be disposed of by means of judicious 

 ventilation. It will be found that by allow- 

 ing the top ventilators to remain slightly open 

 the moisture will be evaporated at almost the 

 same rate as it is squeezed out of the air by 

 contraction due to the falling temperature. 



G. W. 



The Orchid Catalogue of the Julius Roehrs 

 Co., Rutherford, New Jersey, U.S.A., is to 

 hand. Consisting of 36 pages with many 

 excellent photographic reproductions it is of 

 great value to Orchid growers, more especially 

 to those in the United States. In a short 

 cultural note, with which we entirely agree, it 

 is remarked : " Some people still have the 

 impression that Orchids are difiicult to grow, 

 but, with the exception of some few rare 

 varieties, quite the contrary is the case. In 

 fact, they are no more difficult of culture than 

 the ordinary greenhouse plant. In this 

 country (United States) many Cattleyas after 

 finishing one growth will start another, an 

 action which should be encouraged, as these 

 bulbs will be fully developed and ready for 

 flowering." The short English season will, 

 unfortunately, not allow of more than one 

 bulb being made during the year. 



