1921] MEIER—ROOT TIP : 121 
evening, giving a choice of between 200-400 seedlings perday. The 
pots of seedlings were carried to the laboratory where the experi- 
mental work was done. In subjecting the seedlings to the current 
the following method was employed. The seedlings were subjected 
to the current one at a time in a moist chamber (text fig. 1) made 
of plaster of Paris and consisting &E 
of a box 18 cm. high, 10 cm. wide, / 
and 7 cm. deep with one side open. 
A slab of plaster of Paris, cast \ 
to fit closely, was set against the 
open side to serve as a door. 
Through the top of this chamber | 
the two non-polarizable electrodes il 
were inserted. These were made e | 
as described earlier, but in actual 
practice it was also found that 
inserting the copper conducting = 
wires without the zinc and zinc 
sulphate gave no_ polarization | 
2 b&b 
within 30 minutes, and with fre- 
quent changes of the moist kaolin 
was regarded as entirely safe. 
Before setting up the elec- 
trodes, the moist chamber was 
placed in water for 20-30 minutes. 
This insured against the roots _ Fis. 1-—Moist eee 
being exposed to a drying atmos- to to moist kaolin Guoagh glass tubes; 
phere while being exposed to the 4, D, kaolin in contact with extremes 
current. The arrangement of the of i he ye ea i ie — 
conducting wires, together with 04 attached to glass tube of upper 
resistances and measuring instru- electrode by rubber bands. 
ments, are diagrammed in text 
fig.2. Band B', represented as binding posts in the diagram, con- 
sisted in reality of an ordinary lighting socket with key. From 
this socket a cord connected to an ordinary wall socket served as a 
source of current from the 110-120 volt direct current circuit. In 
some cases for added resistance a series plug with 4, 8, or 16 candle 
ns 
