130 D. T. MacDOUGAL AND H. A. SPOEHR 



" false" plasmolysis are abundant, while but little attention has 

 been given to a similar state of affairs which results from loss of 

 water by desiccation as externally expressed by the plant in 

 wilting. Some authors hold the view that when extraction 

 reaches a stage marked by shrinkage of a swollen section, it is an 

 indication that the cells are no longer living, but this may not 

 be taken as a criterion. This point, the stage of irreversible 

 desiccation and death by freezing are all relative to changes in 

 colloidal condition, rather than to simple chemical reactions. 2 



In the course of some work on the imbibition and growth of 

 plants the analyses of which show that the water relations of 

 the protoplasm is determined by the pentosan-protein propor- 

 tion, and that the activities of such living material is not to be 

 simulated by the imbibitional action of the amino compounds of 

 gelatine, attention was paid to the following matters : 



a. Extractions from living cell-masses. 



b. Extractions or solutions of sections of biocolloids. 



c. Acidity of fresh or living tissues. 



d. Acidity of desiccated tissues. 



e. Swelling of fresh sections. 



f . Re-swelling of extracted and dried tissues. 



g. Swelling of dried tissues. 



h. Repetition of swelling and drying treatments. 



These treatments as applied to median slices of maturing 

 joints of Opuntia discata grown at Carmel gave measurements 

 as below at 18°C. The flat joints at 10 to 12 mm. in thickness, 

 and the median portion includes but little chlorophyll. Sections 

 suitable for swelling free from any except the smallest fibro- 

 vascular strands are readily procurable. 3 



2 Lauk, E., Die bedeutung der Elektrolyten fur Quellungsprocess. Biochem. 

 Zeitschr, 37: Hft. 1 and 2, pp. 15 and 58. 1916, and Osterhout, W. J. V., Respi- 

 ration after death. Bot. Gaz. 58: 1918. 



3 All measurements were made by the use of auxographs described in Growth 

 and Imbibition. Proc. Amer. Phil. Soc, 56: No. 4, p. 329. 1917. 



