1921] STRAUSBAUGH—DORMANCY AND HARDINESS 339 
dormant condition, capable of resisting low temperatures, were 
eliminated from the field, and the forms which became dormant 
survived. Thus this coincidence is a direct result of adaptive 
reactions which have become a part of the heritage of the species. 
Kreps (8) succeeded in preventing dormancy by controlling 
culture conditions, and Moriscu (9) could break dormancy at 
will by subjecting the twigs to a water bath at high temperatures 
for a period of 10-12 hours. 
While the knowledge of the external factors which affect 
dormancy gives a clearer comprehension of the phenomenon, an 
intensive chemical and physiological study of the changes in the 
bud at all stages in the growth cycle are required to discover the 
internal changes which parallel or precede the visible external 
changes. From such studies only can.the facts be obtained which 
are essential to a full understanding of the changes that induce 
the rest period, the conditions that obtain during dormancy, 
or the initial changes in the resumption of growth. 
Accordingly this investigation was begun with the object of 
determining some of the conditions which prevail in plum buds 
during the dormant period. Chief attention has been given to 
differences in the degree of dormancy in certain hardy and semi- 
hardy varieties, and to determining what relation (if any) might 
exist between the moisture content or moisture retention of dor- 
mant buds in different species and the relative resistance of these 
buds to low temperatures. 
Material and methods 
All the material used in this investigation was obtained from 
the University of Minnesota Fruit Breeding Farm at Zumbra 
Heights. Three varieties differing in hardiness were selected for 
study. The hardiest form, Assiniboine, is a variety of Prunus 
nigra, and has suffered little if any bud injury in Minnesota, even 
during the severest winters. Tonka is a cross between P. ériflora 
var. Burbank and P. americana var. Wolf. The other variety, 
Stella, which has been used extensively, like Tonka, is a cross 
between P. triflora and P. americana. These two varieties differ 
markedly from Assiniboine in that during the most severe winters 
