140 Extraction of Sap from Plant Tissues 



concentration of the sap extracted from a mass of tissue linder con- 

 tinuous pressure. 



At first WC hoped to secure apparatus suitable for determining, 

 in the case of various tissues, the amount of pressure required for 

 the extraction of given volumes of sap and the concentration of the 

 sap thus secured. This proved unfeasible, at least in prehminary 

 studies ; and we limited ourselves to a consideration of the concen- 

 tration of successive samples of equal volumes obtained under ap- 

 proximately continuous pressure. 



In extracting the sap, the tissue was carefully packed, in masses 

 of about 200 grams, in a heavily tinned hemispherical bowl and 

 forced down by means of a plunger of similar nature, which fitted 

 closely into the bowl when empty. Numerous small perforations in 

 the bowl permitted the escape of the extracted sap without disturb- 

 ing the press. The plunger was forced down by a screw which was 

 very slightly turned every few minutes to maintain a constant drop- 

 ping of Juice. Shallow smooth corrugations on the inner surface of 

 the bowl and on that of the plunger prevented any grinding action 

 between the plunger, sample, and bowl, before the applied pressure 

 became sufficient to hold the mass rigid. The press was capable of 

 exerting pressures of from 80 to 100 atmospheres, continually, until 

 all the available sap was extracted. 



As a basis for comparison, the sap was extracted also from a 

 comparable mass of froren tissue.^ This will be designated as the 

 " original f rozen sample." After the process of sap-extraction had 

 been carried as far as possible by direct pressing, the residue gen- 

 erally contained sufficient water for an ample extraction of sap after 

 being frozen. This residual part of the tissue will be referred to as 

 the " frozen residue." 



The concentrations (osmotic pressures) of all the saps were 

 measured in terms of the depression of the freezing point, as esti- 

 mated by the well known Beckmann method. 



The results of a rather large series of experiments can be stated 

 very tersely, and with illustrative cases instead of with a füll series 

 of observational data. 



3 For methods see Gortner and Harris: Plant World, 17: 49-53, 1914. 



