Andrews. — The Effect of Gases on Nuclear Division. 529 
divide. When, however, nuclei were subjected to a temperature of 1-5° C., 
they finished dividing and formed a cell-wall when in the prophase stage. 
Resting nuclei do not divide at less than J° C., and then very slowly. When 
the nucleus is kept at o° C. for a time and then gradually brought back to 
warmer air, as for example 20° C., the division will be completed and a cell- 
wall formed after three hours. The movement of the protoplasm was not 
visible at a temperature at which the nucleus could not divide. 
VII. Effect of Heat. 
When nuclei in the prophase stage were subjected to a temperature of 
34° C. they finished dividing, but no cell-wall was formed. The time for 
division was increased by one half as shown by the controls. When the 
temperature was lowered to between 20° C. and 30° C. the cell-wall was 
formed. The nuclei always appeared normal, and no tendency to direct 
division, with either heat, cold, or any other agency, was observed. 
VIII. Effects of Ammonium Carbonate. 
Placed directly in a 5 and | per cent, solution of ammonium carbonate, 
the nucleus of Tradescantia virginica , when in the prophase stage, finished 
dividing and formed a cell-wall in fifty minutes. The daughter-nuclei were 
irregular in form. 
In a 1 per cent, solution of ammonium carbonate the nucleus which 
had begun to divide stopped almost immediately. When, after one minute, 
fresh water was again supplied, it began again and completed division. 
If left longer than one minute in a 1 per cent, solution the protoplasm and 
nucleus were killed. 
Summary. 
The foregoing experiments warrant the following conclusions concern- 
ing nuclear division in Tradescantia virginica and the movements of the 
protoplasm in this plant and Momordica Elaterium : — 
1. The protoplasm of these plants cannot move in a pure atmosphere 
of hydrogen or carbon dioxide. 
2. Nuclei in the resting stage cannot divide in pure hydrogen or 
carbon dioxide. When, however, a nucleus is near the close of the 
prophase stage, it may complete division but never forms a cell-wall. The 
further division of the nucleus is only continued till the hydrogen or car- 
bon dioxide kills or disables the protoplasm or penetrates to the nucleus, 
for when the nucleus is just beginning division it cannot complete division 
in pure hydrogen or carbon dioxide. 
3. A very slight pressure (3 mm.) of oxygen is sufficient for the 
nucleus to divide. 
O o 2 
