222 Williams.—Observations on the Action of 
mounted in fresh tap water, and ten stomata, chosen at random, were 
measured for the stomatal ratio, i.e. the ratio of the width to be the length 
of the slit. 
The control was then dealt with similarly, and both strips kept in fresh 
supplies of water, in darkness for twenty-four hours. Fresh measurements 
were then made, care being taken of course to leave each strip over the 
mirror of the microscope for the same interval before beginning the tests. 
Exposure for ten minutes to the Coolidge tube with a reading of two 
milliamps was found to reduce this ratio very perceptibly, while twenty-four 
hours after treatment the difference between experimental strip and control 
was greatly enhanced. On one occasion with more penetrating rays (reading 
one milliamp) the average for the stomatal ratio was reduced to 0*39 against 
a value for the control of 0-55. These results therefore confirmed the view 
that shrinkage was due to decreased sap pressure and consequently to 
changed permeability. 
There was still the possibility that the loss of red colouring might be 
partly due to the destruction of the colouring matter. This was tested by 
preparing a water extract of beetroot to give the same pigment. From this, 
by dilution, a series of concentrations was prepared. 
A tube of extract was then darkened by thick black paper and 
exposed to a strong dose of rays of duration longer than that found to 
cause loss of colour in the plant cell. When the liquid was matched against 
the graded tubes it was found to be unchanged in depth of colour and its 
absorption spectrum was observed to be identical with that of the original 
solution. The fact that the chloroplasts were not affected in this material, 
while those in Vallisneria were found by Lopriore to become yellow, led to 
tests on chlorophyll extracts similar to those on the red colouring antho- 
cyanin being made. 
Exposures up to fifty minutes were made with the Coolidge tube; 
again no change in intensity was discovered, and the absorption spectrum 
was identical with that of the control both immediately after exposure and 
asrain a week later. Where discoloration has been found to occur in other 
plants it is possible the cause has been the action of acids released by the 
changes in permeability and not a direct action of the radiations. 
Attention was next paid to the changes in the appearance of the proto¬ 
plasm on still longer exposures as circulation began to slow down. The 
shrunken surfaces became more and more irregular, and an increased 
amount of light was scattered when the cells were viewed with the ultra¬ 
microscope. In some cells great vacuolation was found. 
Finally a stage was reached when, within three minutes, a solution of 
K 2 Cr., 0 7 of o-i per cent, could produce a precipitate with the tannin of 
the cells. The ultra-microscope showed that this precipitate appeared both 
within the shrunken mass and in the corners of the cells from which the 
