TISSUES AND SIMPLE ORGANS. 10T 



hours before they will diffuse into the surrounding water. There- 

 fore either the molecules of sugar cannot pass through the primor- 

 dial utricle, or more molecules of water pass inward than sugar- and 

 salt-molecules pass out. The latter phenomenon makes it evident 

 that such a plasmic interstice has a certain depth and width, but 

 that water takes a position at the periphery of the same and passes 

 into the cell because of the greater affinity of the saline substance 

 to the water. In the middle of the interstitial canal the salt- and 

 water -molecules move in an equalized or balanced relationship 

 (hydro-diffusion), while in the immediate vicinity of the cell-w T all 

 substance there is an excess of water flowing inward. Hence it 

 matters not whether none or a few sugar- or salt-molecules pass 

 outward : water will accumulate in the interior of the cell ; the 

 hydrostatic pressure of the cell increases; the cell-membrane, 

 which forms the support of the primordial utricle, becomes more 

 and more tense and in return it exerts an equal pressure, due to its 

 elasticity, upon the cell-contents. It is only necessary to assume 

 that at certain points doubtless the thin areas of the cell-wall, the 

 pores the primordial utricle is more readily permeable to water 

 than at other points. If these cells lie in contact with vessels, then 

 the thin areas are comparable to openings at which suction-tubes are 

 placed. If the endosmosis of water in living cells lying near a vas- 

 cular system continues, the infiltration into the vessels will also 

 continue, and the question arises, How high can the column of water 

 be raised? This height is evidently dependent upon the nature of 

 the primordial utricle, on the composition of the endosmotically 

 acting substances, on the relative concentration and temperature of 

 the liquids, and on the diameter of the vessels. Potassium nitrate, 

 for example, possesses a very high " endosmotic equivalent," as 

 has been demonstrated by PFEFFER. His experiments were made 

 with clay-cells, the interior of which were lined with a film of 

 cupric ferrocyanide. For a one per cent potassium nitrate solution 

 the pressure was sufficient to cause the mercury-column to rise 175.8 

 cm. 



If one supposes the forcing in of water to be interrupted, so 

 that water and air pass into the vessel alternately, there is produced 

 the so-called c 4 chain of Jamin. ' ' 



Bleeding (Blutungsdruck) a better term than ' ' root-pressure, ' ' 

 because we are not concerned with any specific activity of the roots 



