38 PLANT PHYSIOLOGY 



to investigation, which I hope some day to install. It is to be 

 composed of tightly jointed plate glass, projecting in part from 

 a southern exposure of the greenhouse, where it is to be covered 

 by an outer case of plate glass, the intermediate space, one foot 

 deep all around, serving for circulation of warm air from the 

 house, and also to hold shades for regulating the light. The 

 plants and instruments will stand on adjustable glass shelves, 

 where they will be lighted from the east, south, and west sides, 

 as well as from above. It is to be 6 feet high by 4 feet square, 

 and therefore large enough for a person to enter (through a 

 large port hole in the inclined bottom) for the arrangement of 

 the apparatus. The temperature, moisture, etc., are to be 

 regulated by drawing the air of the case through accessory metal 

 chambers by electric fans, and these chambers are to be, respec- 

 tively, (a) heated by electric coils, (b) cooled by metal boxes 

 containing ice and salt, (c) moistened by wet sponges, (d) dried 

 by calcium-chloride or sulphuric-acid troughs. I have no doubt 

 the arms of the registering thermograph and hygrograph can 

 be made, as they rise and fall, to open and close circuits which 

 will automatically start and stop the appropriate fans, thus 

 making the whole arrangement self-regulating. It is only by 

 means of such a chamber, in which the conditions can be con- 

 trolled and varied one at a time, supplemented by autographic 

 instruments, that we can separate and determine the effects 

 of the individual external factors upon the plant.* 



Such is an efficient experiment greenhouse, thoroughly built 

 for long service. At present prices it will cost close to $2000, 

 supposing the heat to be available from a neighboring house. 

 Here, as elsewhere, the best is, in the end, the most econom- 

 ical. It can be built much more cheaply by using a wooden 

 instead of an iron frame, simpler tables, and other economies. 

 Indeed, greenhouses can be built of almost any degree of 

 cheapness, and I have been told of one, said to be really efficient, 

 which reaches the limit of simplicity; it is sunken in the ground 



*For studies requiring simply an even temperature and humidity, with dark- 

 ness, an underground chamber would undoubtedly be best. 



