36 PLANT PHYSIOLOGY 



with walls of a single thickness of brick up to 3 feet 6 inches; 

 but above this it will be of glass to the roof, which is to be made 

 of thin, matched boards, painted white above. Inside, against 

 the laboratory wall, will be a slate table holding several Bunsen 

 burners with their supports, and above it a metal hood leading 

 to a protected outlet, as indicated in figure 3. This should ensure 

 the removal of all gases and vapors from the building. Along 

 the wall towards the greenhouse will be the long porcelain- 

 lined sink with the several taps needed for the different appli- 

 ances described later under Apparatus. The short table be- 

 tween the sink and the ventilator is intended for the gas genera- 

 tors with pneumatic trough, while shelves above the sink are 

 'to contain the chemicals in actual use. Ventilation will be 

 provided by the side ventilator, made a part of the room as 

 shown by the figure. Of course the door into the laboratory 

 will close tightly. Being practically wholly inside the green- 

 house, it will need no special heating. 



In any working experiment greenhouse, it is desirable or 

 essential to have a set of recording meteorological instruments, 

 the nature and use of which will later be considered. These 

 are placed on the central table under a simple but efficient 

 cover made of wood painted white, of the form shown in section 

 by figure 4, and in view by Plate I. 



The necessary shading of the house against too great light 

 and heat is provided in part by a coat of whiting placed on the 

 outside of the glass in February or March; it weathers off 

 before the next winter. But an adjustable shading over the 

 south side is given by cotton shades, which rest upon wires 

 close to the roof, and are drawn up by cords running over pulleys. 

 The system does not, of course, give intermediate gradations 

 of light, as could be provided by some system of swinging shades, 

 but it has proven efficient for all ordinary purposes. 



The final furniture of the experiment greenhouse consists 

 of a case in which, for special purposes, light temperature and 

 moisture, especially the two latter, may be kept stable or varied 

 at will, a modification of the Wardian case which may be termed 



