8o 



PROTOPLASM 



nevertheless without importance for the explanation attempted 

 by me. My explanation does riot deal with the absolute amount 

 of the surface tension, but with its differences at different spots 

 on the surface of the drop, and these differences may remain the 

 same even when the absolute quantity of surface tension is 

 diminished. 



8. Streaming Movements exhibited by Drops of Foam 

 in Cells 



With regard to the streamings of protoplasm within 

 plant cells, it seemed to me important to try what form the 

 streamings might take in froth-drops which were contained 

 in small closed spaces. This experiment was carried out as 

 follows. Moderately thin sections of elder or sunflower 

 pith were passed from absolute alcohol into chloroform, and 

 then into an oil suitable for the formation of froth. The 

 cell spaces of the pith became completely filled with oil in 

 the process. In order to drive off the chloroform entirely, 

 the oil was allowed to stand with the pith sections in a warm 

 case for some time at a higher temperature. The sections 

 soaked with oil were well washed out with water and brought 



into a 1 to 2 per cent solution of 

 K 2 C0 3 , either under the cover glass 

 or in a small test tube. After 

 twenty-four to forty-eight hours 

 the oil was milk-white, and of a 

 fine foam -like structure through- 

 out. The sections are again washed 

 with water, and finally freed from 

 any oil -foam adhering to them 

 externally by being brushed with a 

 paint-brush. They were then put 

 up in semi- dilute glycerine. In 

 successful preparations it is then observed that the oil-lather 

 contained in each of the pith cells is in lively streaming, 

 which persists for some hours. Since the glycerine dimin- 

 ishes the volume of the oil-lather, the cells are never 

 completely full, which disturbs the approximation to the 

 conditions of the plant cell (see Fig. 17). The phenomena 



