356 BOTANICAL GAZETTE [may 
definite relation between dormancy and hardiness. Assiniboine 
is extremely hardy and its dormancy is very profound, in contrast 
with Tonka and Stella, two semihardy varieties in Minnesota, 
which appear to enter real dormancy for only a very short period 
in early winter, if they do so at all. 
2. During the period of dormancy the moisture content of the 
semihardy varieties fluctuates with the temperature. Periods of 
low temperatures are accompanied by a loss of moisture from the 
leaf and fruit buds, and higher winter temperatures, which are 
seldom above freezing in Minnesota, by an increase in moisture 
content. In comparison with the semihardy varieties the moisture 
content of Assiniboine remains at a definite and fairly constant 
minimum throughout dormancy. 
3. When the fluctuations in the moisture content of buds were 
found to occur under orchard conditions, this phase of the problem 
was checked under control in the laboratory by placing the twig- 
bud-system in sealed chambers over different concentrations of 
sulphuric acid. By this method water movement in the tissues 
of Assiniboine was found to take place more slowly than in Stella 
and Tonka. lLenticel number per unit area was found to be cor- 
related with the difference in moisture retaining capacity. 
4. Somewhere near the mid-point of the dormant period funda- 
mental metabolic changes occur which affect the ecological reactions 
of apparently dormant plum trees in a striking manner. As 4 
result of these changes, or at least coincident with them, winter 
killing in the flower buds is found for the first time, the moisture 
retaining capacity of the fruit and leaf buds is changed, and anthesis 
occurs when fruit buds are subjected to favorable growth tempera- 
tures in the greenhouse. These changes are interpreted as indicating 
the time when the rest period is broken. 
5. The dormant condition reached by the hardy forms, such as 
Assiniboine, appears to involve fundamental protoplasmic changes. 
Among these there may be a change in colloidal properties creating 
an increased imbibition which may account for the marked retention 
of water against the force of dehydration. 
6. This investigation has a direct bearing upon the applied 
problem of selecting seedling fruits for hardiness. A study of the 
