Protoplasm to some Reagents. 
491 
but also of different leaves on the same shoot, and of different shoots in one 
lot of plants, and again, of different lots collected at different times and in 
different localities. 
What all the controlling factors are, it is impossible to say. One or 
two of them were, however, ascertained. Young and luxuriantly growing 
Elodea plants are less resistant to alcohol than are older plants. Also, the 
longer the time plants remain in culture in the laboratory the greater does 
their resistance to alcohol become. (The osmotic pressure of the cell is 
likewise increased.) 
The variability in reaction of the different cells of the same leaf can 
only be attributed to different physiological states of the cells, the causes of 
which are as yet unknown. 
This variability in behaviour of the cells of Elodea leaves made it 
necessary to make many observations in order to obtain a general average 
of behaviour. Only such grand averages, unless otherwise stated, are given 
in this paper. In most instances these averages are based on the observa¬ 
tion of more than a hundred leaves, representing many thousands of cells, 
for each time of treatment in every concentration of the several re¬ 
agents used. 
The average length of time necessary to kill an Elodea protoplast 
with io per cent. (1*7 M) ethyl alcohol is about (slightly less than) half 
an hour. In the most resistant leaf found every cell withstood the harmful 
effect of 10 per cent, alcohol for two hours, not a single dead cell being 
found. That the cells suffered to a considerable extent, which was not 
superficially noticeable, is inevitable. Such extreme resistance is, however, 
rare. In only one leaf in a hundred do all the cells survive the toxic effect 
of 10 per cent, alcohol for one hour. In contrast to these instances are 
those of two other leaves, in one of which 97 per cent, of the cells were 
killed in 10 per cent, alcohol in half an hour, and in the other, 99 per cent, 
were killed in one hour. 1 
The curve in Fig. 2 depicts the average rate at which a 10 per cent, 
solution of ethyl alcohol kills the cells of Elodea. The ordinates are 
minutes and hours of treatment in the alcohol. The abscissae are percentages 
of cells killed. It will be seen that in the average Elodea leaf no cells are 
1 The criterion of death used was inability to plasmolyse with a 10 per cent, solution of potassium 
nitrate. The average critical plasmolytic concentration, i. e. that concentration of plasmolysing 
salt which will, in a half-hour, plasmolyse about 50 per cent, of the total number of cells in a leaf, is 
3 per cent. KNO s ; therefore it is reasonable to assume that a cell incapable of plasmolysis with 
10 per cent. KNO s is dead. To prove the truth of this a 20 per cent, solution of potassium nitrate 
was applied after a 10 per cent, solution, and no additional cells were plasmolysed. To further 
convince myself that these alcohol-treated cells which could not be plasmolysed with 10 per cent. 
KN 0 3 , were dead, I observed whether or not cells treated in 10 per cent, alcohol for twenty minutes, 
half an hour, and one and a half hours would recover. There was no recovery after three days in 
water. Other indications of death are also usually present, such as an irregularly shrunken 
(coagulated) and discoloured protoplast. 
