1921] STRAUSBAUGH—DORMANCY AND HARDINESS 351 
three days the loss in all cases was found to be practically negligible, 
the greatest loss being only 0.7 gm. from a total weight of 137.47 
gm., ora little more thano.5 percent. Thus it seems quite evident 
that there is little exchange of moisture between the air and the 
tissues of the twigs due to evaporation alone, but that some dehy- 
drating force is necessary to account for such losses as have been 
shown to take place in connection with low temperatures. 
In the studies of water loss from twigs in the acid chambers and 
also by the fan method, a conspicuous structural difference in the 
bark of the hardy form as compared with that of semihardy forms 
became evident. This difference may possibly be associated in 
some way with the slower movement of water in the hardy variety. 
The twigs in all three of the forms studied are covered with a heavy 
suberized layer which renders them impervious to water except 
through the lenticels. The number of these lenticels per unit 
surface is fairly constant for a given variety, but a marked difference 
is observed between hardy and semihardy varieties. Five separate 
counts were made on sections of twigs of Stella and Assiniboine. 
The sections chosen were 5 cm. long and 1.2 cm. in diameter, 
representing in each case a curved surface area of 18.85 sq. cm. 
Table IX gives the result of these counts. 
TABLE Ix 
NUMBER OF LENTICELS PRESENT ON 18.85 SQ. CM. 
OF TWIG SURFA 
STELLA ASSINIBOINE 
49 12 
54 Io 
48 8 
39 13 
54 Ii 
As these lenticels are approximately the same size in each 
variety, it will be seen that the total lenticel area in the semihardy 
form is from 3 to 6 times that occurring in the hardy variety. 
The exact significance of this marked difference in bark character 
is not fully clear, but that it may be related in some way to the more 
tardy movement of water from the twigs of Assiniboine is a 
possibility that seems worthy of consideration. 
