12 Wilder Wluat Varieties aitil Winter- Killing 



DISCUSSION. 



The depression of the freezing point A, the corresponding osmotic 

 pressure P, and the hydrogen-ion concentration of the sap of the samples 

 collected October 29 are given in Table II. The osmotic j)ressiires recorded 

 are based on the freezing ])oint data, use being made of tiie ]iublished 

 tables of Harris and (!or^ner(l^). The hydrogen-ion concentration is 

 expressed in terms of pW value as read from the tables of Schmidt and 

 Hoagland(4i). A classification of varieties, as determined by survival 

 under field conditions during a nund^er of years, was supplied i)y the 

 Department of Plant Breeding and is included in the table. It will be 

 seen that in this collection at least there are no significant variations in 

 the constants reported which could be correlated with the relative hardi- 

 ness of varieties. 



The same absence of correlation in pliysiial constants, including 

 specific conductivity A', holds true for the collection of Novendjcr VI. 

 reported in Table HI. It may be noted, however, that the concentration 

 of the sap had increased somewhat in the varieties used. In the collection 

 of December 9, included in the same table, all varieties exhibit a faUing 

 off in the depression of the freezing point and corresponding osmotic 

 pressure, probably due in part to simple dilution of the sap, as the 

 moisture content of the tissue was greater. One variety, Kanred, fell 

 off in this respect appreciably more than the rest. It is perhaps note- 

 worthy that this variety winter-killed somewhat more tiian tlie others 

 during the year of this test. 



An unexpected difficulty was encountered in expressing the sap from 

 the sam])les collected Decend)er 9. The samples were frozen by the 

 method already described, using a freezing mixture of pulverised calcium 

 chloride and snow mixed in the ju'oportions wliich should give theoreti- 

 cally a cryohydrate mixture with a corresponding temperature of 

 — 54-9° C. After seven iiours' freezing, the samples were thawed under 

 running water, and refrozen for a period of 1 1 hours. They were thawed 

 again under the tap. Even after this treatment it was found impossible 

 to express more than 2 to 3 c.c. of juice from 100 grams of material under 

 400 atmospheres pressure. Further, the plants retained their bright 

 green colour instead of a.ssuming the w'atersoaked appearance character- 

 istic of fiost-kiiled tissuc^s. The data of Table V show that these samples 

 contained a lower percentage of dry matter than did the earlier collection, 

 consequently the failure to express the sap was not due to lack of moisture 

 in the tissues but apparently to a failure to break down the colloidal 



