Studies oe Heaeth in Potatoes. 
15 
the potato plant. Pc seems probable that the potato' plant was 
developed by nature on deep, sandy loams in an equable maritime 
climate. Our mountain potato districts are among the best in the 
world because of their cool temperature, pure, cool water, abundant 
slope, and fertile, alfalfa-filled soils. They would be still better for 
potatoes if their air was damp. 
III. GREENHOUSE STUDIES OF SOIL TEMPERATURES 
AND MOISTURE. 
Following the field evidence that soil heat or soakage, or both, 
had been the occasion of the leaf-roll disease, arrangements were 
made for the study of these factors under controlled conditions 
(Figure 2). A preliminary experiment, in which large incubators 
heated with lamps were used, having proven unsatisfactory 
because of the impossibility ol securing natural conditions of 
air and light, four cabinets (Figure 2) were made and fitted with 
racks, for the suspension, in a water bath, of watertight tanks in 
which potatoes were planted. Each cabinet held 35 tanks, the space 
which otherwise would have been occupied by the 36th tank being 
given to the electrical heating* and turbine stirring arrang'ements 
shown overhead in Figure 2. Six-hundred-watt heating units, 
such as are used in electric irons, were soldered tO' lead pipes which 
protected the connections. The unit was placed in the water directly 
beneath the turbine wheel, which was set vertically and arrang'ed to 
draw the water upwards past the heating unit. Power was furnished 
by a water motor running continuously. One tank in each cabinet 
was given to the thermostat which operated the magnets, and these, 
in turn, cut the heating* current out and in. In the coldest cabinet, a 
geared electric switch was used to open and shut a valve in a pipe 
supplying mountain water at about 33 degrees F. Except for 
some weakness in construction of the switches, all the mechamVal 
and electrical parts nroved to do their work well. The turbine 
arrangement was particidarlv sati'^factorv and maintained the tem¬ 
peratures in the farthest corners of the cabinets just the same is in 
the center. 
The tanks held 23 pounds each of calculated dry earth. Each 
empty tank was made un to even weight with coarse sand and this 
sand was used to mulch the earth and prevent puddling while 
watering. The tanks and calculated drv earth all weighed the same 
and a lead weight was made to balance this amount. By sacrificing 
at intervals some six plants and iveighing them, we were able to 
set, on the second beam of our scales, our idant tare and weigh the 
