1921] STRAUSBAUGH—DORMANCY AND. HARDINESS 355 
(figs. 1, 2 and table VII). The point that must be emphasized, 
however, is that the hardy buds have the capacity to retain their 
moisture at a certain definite and fairly constant minimum through- 
out the period of dormancy regardless of all fluctuations in tempera- 
ture, and that this capacity is not a characteristic of the semihardy 
or tender buds. WHEGAND (12) states as follows: 
Every cell has its critical point, the withdrawal of water beyond which will 
cause the death of the cell, whether by ordinary evaporation or by other means. 
It may be supposed that the delicate structure of the protoplasm necessary 
to constitute living matter can no longer sustain itself when too many molecules 
of water are removed from its support. aoe the great majority of plants this 
point lies so high in the water content 1 very soon after the incep- 
tion of ice formation, hence the death of so many plants at this period. Others 
may be able to exist with so little water that a very low temperature is necessary 
before a sufficient quantity is abstracted to cause death. From some plants 
enough water cannot be extracted by cold to kill them. 
The hardy plum, Assiniboine, lies very close to the last men- 
tioned class of plants. It requires exceedingly low temperatures 
to cause it injury, and the explanation of this fact seems to lie 
in its ability to retain its moisture. Water movement in its 
tissues seems to be much slower, so that it matures earlier in the 
autumn and assumes its maximum water content more slowly in 
the spring. The fact that it blooms from two to three days earlier 
than the semihardy varieties may be due to the possibility of 
growth activities taking place with a much lower water content. 
The moisture relations that obtain between the hardy and 
semihardy buds of the plum indicate a wide difference in their 
physiological reactions. These reactions arise from specific con- 
ditions within the cells, and therefore it is assumed that the pro- 
toplasmic structure of the hardy tissues is different from that of the 
semihardy tissues. These differences are inherent, so that they 
furnish a basis for the work of the plant breeder. There is a 
suggestion here, therefore, that a study of the moisture relations of 
seedling plants during both the dormant and vegetative conditions 
may afford a tentative basis for determining selections. 
Summary 
1. In the plum there are widely differing degrees of dormancy. 
among the different species and varieties. There appears to be a 
