392 BOTANICAL GAZETTE [NOVEMBER 
So many requests for information concerning the apparatus have - 
been received that it has become impossible to give individual 
replies. 
The apparatus consists of a metallic thermostat (fig. 1) placed 
on a shelf in the oven, a water-jacketed heating coil (fig. 2) fastened 
to the bottom of the oven in such a way that the water jacket of the 
coil forms a continuous system with that of the oven, and an auto- 
matic switch (fig. 3) placed wherever convenient. 
The thermostat (fig. 1, 2) is a thin strip of iron about 1 mm. thick 
and 2 cm. wide, firmly riveted to a strip of zinc the same width and 
nln 
Fic. 1.—Diagram of thermostat and connections; , thermostat of zinc and iron; 
d, screw for adjusting temperature; 5, b’, binding posts to connect with #, ¢’ of the 
switchboard. 
from 1.5mm. to 3mm. thick. One end is fastened to a brass post 
set rigidly on the slate base, and the other end swings free. The free 
end of the metal tongue has a contact point of platinum fastened 
to the zinc side near the end. The adjustment for temperature is 
made with a platinum-tipped screw (d) set so that its point can 
always be brought in contact with the platinum disk on the metal 
tongue. The metal tongue and the adjusting screw are connected 
respectively with the binding posts (8, b’), as shown in the diagram. 
The base of the thermostat should be made long enough to fit 
easily in the oven, the ends resting on ledges provided for the upper 
shelf. The sensitiveness of the thermostat depends, of course, on 
the length of the metal tongue. If extreme sensitiveness is requir ed, 
it may be made nearly twice the length of the base and bent toa U, 
or it may be much longer and coiled. In practice 20 cm. has been 
found satisfactory. The zinc strip should not be thinner than 
