322 BOTANICAL GAZETTE [OCTOBER 
The bottom of the Petri dish is ruled into 5 mm. squares. The 
squares not only aid in determining the angles made by the bending root, 
but also serve as markers to 
= locate the regions of growth 
Z HAA tS and curvature. A sheet of 
J U pK , coordinate paper pasted 
Y 4a At 4 over the bottom of the dish 
Ef will serve nearly as well as 
3 Zs the cross-ruling. Thin 
! paper, such as is used for 
Lt 44-4] making blue-print tracings, 
444] is best. The paper can be 
AG made more transparent by 
wetting it with a mixture of 
alcohol, glycerine, and water. 
ae Seedlings may be grown 
\ for a number of days in the 
chambers. It is possible, 
therefore, to place the seed- 
lings in the chambers some 
time previous to the time 
set for the experiments. If 
the filter paper lining the 
»)) chamber is placed symmetri- 
“i cally, so as to avoid hydro- 
= Mill | tropic curvatures, the 
radicles will grow straight 
downward. The chamber 
can now be rotated and the 
seedling quickly brought to any desired angle with the vertical, and 
without exposing it to the dry air of the laboratory. The chambers 
are excellent for experiments on perception and latent periods, and for 
periodic responses—W. T. Bovis, Laboratory of Plant Physiology, 
Harvard University. 
Ur : 
Fic. 3 
