Note . 
557 
It would no doubt be advantageous for the under surface of the cork disc and the 
upper surface of the cork on which it rests to be faced with some harder and more 
accurately plane surface than cork. A microscope cover-glass with a hole drilled 
through the centre should serve. Another drilled cover-glass forms a convenient 
washer. 
(2) If the experiment is continued for more than a few hours, the water surface 
may be measurably lowered as a result of evaporation — the water vapour condensing 
on the inside of the jar. Error from this cause can be eliminated in the following 
way. A piece of glass tubing is drawn out to a fine capillary, sealed at the end, and 
inserted through the cork (h, Fig. I). The height of this is adjusted until the lower 
end is about the same level above the water surface as the tip of the root. Whenever 
the position of the glass rod which causes contact of the water surface with the root is 
determined, that which causes contact with the end of h is also noted. Thus, the 
position of the root tip is measured at successive intervals in relation, not to the water 
level, but to the end of h, which is a fixed point. Alteration of the water level during 
the experiment is thus of no importance. 
(3) For prolonged experiments it will be found advisable to have a slow stream 
of air bubbling through the water in the jar. This provides aeration for the root and 
also ensures that the atmosphere around the root is kept constantly moist. 
W. NEILSON JONES. 
Botanical Laboratory, 
Bedford College, * 
July , 1920. 
