1917] HARRIS & LAWRENCE—TISSUE FLUIDS 289 
of tissue were collected in test tubes of about 100 cc. capacity and 
taken to the laboratory for freezing by immersion for several hours 
in an ice and salt mixture, in order to avoid errors in the extraction 
of sap as noted by Drxon and Arxins’ and ourselves.’ The sap 
was then extracted by pressure in a small heavily tinned press bowl 
with a powerful hand screw. After filtering, the freezing-point 
lowering of the sap was determined by the use of a thermometer 
graduated in hundredths of degrees with divisions sufficiently large 
to permit reading approximately to thousandths of degrees. 
In some instances a cloudiness or flocculent precipitate similar 
to that described by GorKE? was observed when the sap approached 
the freezing point or passed it in undercooling. We had no facilities 
for any investigation of these substances, but believe their pressure 
does not greatly, if at all, influence our results. 
The measurements are recorded in degrees depression (A) 
corrected for undercooling and in atmospheres pressure (P) from a 
table published elsewhere.” The fact that a number of the deter- 
minations exceeded the range of the table as originally printed has 
led to the publication of a supplementary one." 
Presentation and analysis of data 
In the following protocol the values to the extreme right opposite 
the species names are (whenever possible) averages. These averages 
are designated by bars. The individual readings upon which they 
are based, with their dates of collection,are entered below the species, 
except in the cases in which only a single determination is available 
and must serve, instead of an average, to represent the species. 
7 Drxon, H. H., and Arxins, W. R. G., Osmotic pressures in plants. I. Methods 
of extracting sap from ont ores Sci. Proc. Roy. Dublin Soc. N.S. 13:422-433. 
1913; alsoi h. Trin. Coll. Dublin 2:154-172. 1913- 
§ Gortner, R. A. piiceen i V., and Harris, J. ArtHUR, The extraction 
of sap from ae tissues by pressure. B iochem . Bull. 5:139-142. pl. I. 1916. 
° Gorxe, H., Uber chemische Voeskhee beim Erfrieren der Pflanzen. Land- 
seas Wecual Stat. 65:149-160. 1906. 
* Harris, J. ARTHUR, and GorTNER, R. A., Note on the apc of oa — 
reprinted in Matrnew’s Physiological Chemistry. 
™ Harris, J. ARTHUR, An extension to 5. 6s ot tables to determine the osmotic 
Pressure of exp: of the freezing point. Amer. 
Jour. Bot. 2: 2418-419. 191s. 
