GROWING BACTERIOLOGICALLY STERILE POTATO PLANTS 9 
At the left of the center is shown the calibrating plunger X. This 
consisted of a %-inch threaded pipe, closed at the end within the 
cylinder and fastened outside with a lock nut. The plunger was 
screwed in or out as was necessary to cause the cylinder to deliver 
precisely 2 liters of water in operation. 
The flexible metal hose or pipe, mentioned as coming from the 
swivel Z at the bottom of the cylinder, was the right external diameter 
to fit inside of the %-inch pip e m the can cover, shown in Figure 1. 
At a point 2}/± inches from the end of the pipe a sheet-iron cuff was 
soldered, which was large enough to fit closely over the outside of 
the %-inch pipe of the can cover, and extending over it on the out- 
side as far as the flexible pipe did on the inside. When the flexible 
pipes were not in use the ends were encased in a close-fitting metal 
box or mitten, drawn tight with thumbscrews. 
Plate 3, A, shows the method of attaching the flexible metal pipes 
of the watering machine to the can covers. 
MINOR EQUIPMENT 
SOIL THERMOMETER 
As shown in Plate 3, A, recording thermometers were supplied to 
some cans. These were the common type of soil thermograph, 
recording on the paper of a cylinder rotating once in a week. 
WATER TROUGH 
In Plate 3, B, the cans are shown submerged in water for the pur- 
pose of lowering the temperature. 
The trough was built of concrete. The interior dimensions were 
42 feet long, 2 feet wide, and 2^2 feet deep. Each side accommodated 
25 cans. The water was taken from an irrigation ditch 125 feet 
away and was pumped in and out at will by a centrifugal pump 
driven by an electric motor. A single trough with cans in place 
could be filled with water in 20 minutes. 
LAMP CHIMNEY 
The lamp chimney which appears in Plates 3, 5, and 6 was 10 
inches high and made of heavy clear glass. The top was straight 
and smooth, and the top opening was filled with a tight cotton plug 
having a cork in the center to give it form. 
GASOLINE BLOWTORCH 
Two hand gasoline blowtorches of the kind used by plumbers were 
in constant use. The gasoline was vaporized and ejected under 
pressure into a Bunson-type burner and delivered a flame of great 
heat intensity. They were not fully reliable, so two were always in 
readiness, even though only one was needed. Steam, wind, or lack 
of air would sometimes suddenly extinguish one at a critical time, so 
a second one was always lighted and ready for such an emergency. 
There were some other minor pieces of apparatus used in the exper- 
iment, but not of enough importance to be recorded. Their use 
depended on the wish of the operator and not on any imperative 
demand of the experiment. 
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