20 



central cylinder with the twigs or woody tissue and the thermometer 

 on its surface was kept slowly revolving by means of a small electric 

 motor. During the freezing, this was stopped only for thermometer 

 readings which were taken generally every fifteen minutes. 



Method of Determining Freezing Point of Sap. The density 

 of sap was determined by means of a Beckmann Freezing Point Appa- 

 ratus. The tissue was ground in an ordinary food grinder, using the 

 knife that grinds the finest, and the sap was expressed with the appa- 

 ratus shown in Figure 3. The large block with the hole in the center 

 is of sugar maple which will not split readily. The smaller block 

 is of the same material and is made to fit in the depression in the large 

 block leaving about one-eighth of an inch surrounding space. The 

 ground tissue was wrapped in a clean piece of eight or ten ounce duck 

 and put in the depression in the large block, the small block put 

 against it and the two pressed together between pieces of 4x4 lumber 

 drawn together by a pair of bench screws as shown in the figure. 

 The sap could be expressed very quickly. With succulent plants 

 loss by evaporation in all cases was negligible. In the case of leaves 

 of peaches it required a considerable length of time for the sap to 

 exude. 



In all cases before plants with different treatments were frozen 

 or before they were ground for expressing sap, they were, after being 

 pulled, kept with the roots in a glass of water until they became 

 apparently turgid, since wilting sometimes seems to reduce slightly 

 the killing temperature, and would appreciably affect the sap density 

 determinations. 



EXPERIMENTS WITH SEEDLINGS OF ZEA MAYS 



A large number of corn seedlings were grown and frozen. The 

 following table gives the date of freezing, the solution with which 

 the material was watered, the temperature to which the plants were 

 subjected, the percentage killed and percentage partly killed, and the 

 freezing point of the sap. The freezing point is given as depression, 

 meaning the number of degrees below zero, centigrade, at which ice 

 begins to form in the sap, assuming no supercooling. 



