522 Andrews . — The Effect of Gases on Nuclear Division . 
least within the limits which concern us here 1 . A stronger solution 
of cane sugar (5 per cent.) may, as Hormann 2 has shown, cause a retarda- 
tion of protoplasmic movement in a cell of Nitella. It was also very 
noticeable that the movement of the protoplasm in the younger cells 
of the staminal hairs was more readily and quickly affected by the 
influence of various gases than in the older cells whose cell-walls were, 
as one would naturally suppose, less permeable. This disregard of the 
age and condition under which the plant-cells live, and the attempt to 
apply the same tests to different plants and obtain similar results, has led 
to numerous errors on the part of many investigators. 
Great care has been necessary in these experiments. The perfection 
of the apparatus, and the nature of the plant-material it was necessary 
to use, would make it at once evident to any one at all conversant with 
such a subject as this how very difficult it often is to arrive at a definite 
and certain result. In order to be sure that my results were correct, 
I have repeated each experiment several times. 
It is not surprising then that Demoor made mistakes in some of 
his experiments and conclusions. While his general methods were good, 
he did not take sufficient precaution to obtain gases that were absolutely 
pure. The same lack of care in obtaining absolutely pure gases caused 
Lopriore 3 to make some mistakes in his experiments and to arrive at entirely 
incorrect conclusions. 
The only way to ascertain that no oxygen remains about the specimen 
under investigation is by means of the Bacterium-method of Engelmann. 
Pure cultures were obtained according to the method given by Detmer 4 , 
and these were used in all my experiments with hydrogen. It is certain, 
as I shall show later on in this paper, that even a very small quantity 
of oxygen is sufficient to allow the nucleus to commence and continue its 
division normally. Since, however, by the excessively delicate reaction 
shown by the Bacterium-method the billionth part of a milligram of 
oxygen can be detected 5 , I was thus able to ascertain the slightest trace 
left in the apparatus or if any should be evolved by the plant-cells under 
observation. 
The natural evolution of oxygen by chlorophyll-bearing cells intro- 
duced another difficulty, but nevertheless made it absolutely necessary 
to avoid using any cells containing even a trace of chlorophyll. 
Since absolute purity of the gases employed is essential for obtaining 
correct results, the utmost precaution was taken to construct apparatus and 
to use only those chemicals that would attain that end. 
1 Ewart, on the Physics and Physiology of Protoplasmic Streaming in Plants, 1902, p. 59. 
3 Studien iiber die Protoplasmastromung bei den Characeen. Jena, 1898, pp. 51-5. 
8 Jahrb. f. wiss. Bot., 1895, Bd. 38, p. 531. 
4 Pflanzenphysiologie, 2. Aufl., 1895, p. 32. 
5 Pfeffer, Pflanzenphysiologie, 1897, 2. Aufl., Bd. 1, p. 292 and literature cited there. 
