40 MACDOUGAL— ACTION OF LIPOIDS IN GROWTH. 



thickness was desired, this was continued until all of the jelly had set. 

 If a thinner layer was required, the stopper was removed after two 

 or three minutes and most of the liquid poured out. Uniformity was 

 attempted in the cells in any series. 



After cooling for ten minutes, the cell contents were poured in 

 and the preparation set in the immersion solution so that the outlet 

 tube was horizontal and no siphoning action was possible. Readings 

 were generally made at 24-hour intervals unless otherwise specified. 



The clay thimble is so readily permeable to salts of potassium and 

 sodium at o.oiM that no action of this wall alone followed a filling 

 with such solutions except a direct outward diffusion. It is much less 

 permeable to organic compounds, such as sugar, asparagin, saponin, 

 soap, etc. A comparison of its action with the results given by 

 Bartell would seem to indicate that the clay wall has pores less than 

 I IX. in diameter.^ The positive action of the thimble with sugar may 

 be illustrated by the fact that when filled with a 2 per cent, solution 

 and immersed in water at 18° C. a column 3 mm. in diameter was 

 raised to a height of 35 mm. in 30 minutes. Asparagin, saponin, and 

 urea at o.oiM also gave positive pressures.^" 



Solutions of agar 0.3 per cent., of gelatine and of potassium oleate 

 as cell contents resulted in endosmose in clay thimbles without any 

 lining layer. Further tests showing the negative osmose which might 

 take place through the walls of the clay thimbles were made with 

 calcium solutions. One lot of thimbles were filled with CaClg at 

 0.0 1 M and set in water, while an equal number were filled with water 

 and set in the calcium solution. The calcium solution inside the cell 

 set up negative osmose which retracted the horizontal column of 

 water in the outlet tube, and the cell containing water showed exuda- 

 tion caused by the passage of water through the walls from the calcium 

 solution in which it was immersed. 



Tests with cylinders of turned wood with walls 3 mm. in thickness 

 showed positive osmose when filled with the calcium solution, as did 

 also filter paper thimbles (double thickness Whatman). It is evi- 

 dent, therefore, that this negative osmose is to be attributed to the 



^ Bartell, F. E., " Pore Diameters of Osmotic Membranes," Jour. Phys. 

 Chem., 16: 318, No. 4, April, 1912. 



10 Stem, K., " Ueber negativen osmosen und verwandten Erscheinungen," 

 Ber. d. Deut. Bot. Gcs., 37: 334-343, I9i9- 



