Chapter VII 



— 103 — Osmotic Quantities of Cells 



It therefore appears that values obtained by this method and reported in the litera- 

 ture are open to some question. 



Strip or Simplified Method: — The advantage of the strip method (Ursprung, 

 1923) is that the measurement embraces hundreds of cells and is more successful in 

 estimating the average DPD of organs. Tissue strips in size approximately 20 mm. 

 long and 2 mm. wide are removed from leaves, stems, or fleshy storage organs. Fila- 

 ments and slender roots are cut into suitable lengths. Vascular elements should not 

 run parallel or at right angles. The length of the sections in paraffin oil is imme- 

 diately determined by means of a microscope and a stage micrometer ; the strips are 

 then transferred to a series of sugar solutions. The DPD of the water in the tissue is 



2 ^ 6 S /O /£ /4 /6 /S £0 22 24 26 28 JO J2 



Osmo/'/c Pressure (oJ^m. a/^ ^O*^ C) 



Fig. 34B. — Diffusion pressure deficit values determined by the 

 weight method. (Meyer and Wallace, 1941). 



equivalent to the OP of that solution which effects no change in length. Usually 30 to 

 45 minutes is sufficient time; often 5 to 10 minutes is enough. 



A simple modification of the above method is useful where massive tissues are 

 studied (Lyon, 1936). CyHnders of tissue 5 to 10 mm. in diameter and several centi- 

 meters long are removed from organs by means of a cork borer, and are immediately 

 measured for length by means of a binocular dissecting microscope fitted with an 

 ocular micrometer. They are then distributed among sucrose solutions of varying con- 

 centration. After several hours, the solution in which the cylinders show no change in 

 length is assumed to be equal in DPD to the tissue. In place of tissue cylinders, square 

 sticks may be used, prepared by means of a double-bladed knife (Lyon, 1940). Check 

 strips are kept in paraffin oil. 



Instead of measuring length changes, volumes may be determined by an immersion 

 method. Cylinders of tissue upon removal from organs are immediately immersed in 

 calibrated glass tubes partially filled with sugar solutions. A diameter of 10 mm. is 

 a convenient size for the tubes. The sugar solutions are in a graded series of known 



