K. Newton 5 



EXPERIMENTAL. 

 The Problem. 



The present study seeks to establish a chemical or ijhvsico-chemical 

 measurement of hardiness for winter wheat varieties. A number of 

 varieties originated or selected by the Department of Plant Breeding of 

 the University of Minnesota, and known to vary considerably in hardi- 

 ness, were compared with reference to the physical constants of the 

 cell sap, the content of amino nitrogen, water-soluble nitrogen and total 

 nitrogen, and the content of sugars and starch. AH materia! used was 

 grown in field plots under normal conditions. Since it was desired to 

 compare the varieties in the hardened condition rather than to study the 

 hardening process, collections were not made until after the advent of 

 freezing weather. 



A preliminary study of physical constants was carried out with eight 

 varieties. Subsequent stud}^ was confined to four of these, two hardy 

 and two tender. One variety, Minhardi, was collected from two plots 

 some distance apart, and these are reported separately as the effect of 

 location was quite marked, 



Metho]is. 



Collection of Samples. All the samples of one series were collected 

 from the field the same afternoon, though with the exception of the 

 first series the leaves were frozen solid when collected, so that changes 

 due to vital activities would be very slight. The plants were growing in 

 rows, which were carefully gone over for the removal of dead leaves 

 before taking the samples. For the collection of November 12, 1920, 

 ib was necessary first to brush off a Hght covering of snow. As the leaves 

 were cut, they were thrown on a wire screen for the removal of adhering 

 bits of dirt and ice, then transferred at once to tight glass containers. 

 Samples of approximately KIO grams were collected in duphcate, one 

 lot for the study of physical constants, the other for analysis for nitrogen 

 and carbohydrates. All samples were kept frozen until used. 



Physical Constants. The depression of the freezing point of the hrst 

 collection was determined by the thermoelectric method, the accuracy 

 of which has been shown by White (I7). The convenient arrangement of 

 apparatus illustrated by Harvey (20, Fig. ]) was used. The leaves were 

 packed into a section of thin-walled glass tubing 2 cm. long, in which 

 they were held in place by a small rubber band, the thermocouple then 

 being inserted in the centre. Undercoohng seldom amounted to more 



