1886.] BOTANICAL GAZETTE. 207 
vals of a few days, from April 30 to May 30, showed little change 
except in the increased growth of the woody portion. In the 
_ Resin passages in the cortex of the young shoot of the white 
pine are cylindrical and have no walls of their own, being 
bounded simply by the surrounding cells, which are all thin- 
tree May 6. As the stem grows, the tube, small at first, may be- 
come larger by division of the cells adjoining it. After a time it 
project into its cavity, the walls of the cells outside the epithe- 
lium thicken and by the pressure of the parts about it as the stem 
From May 6th (fig. 5) up to May 30th there was little change 
to 
P 
surrounding cells having become ver, thick. 
~ : : ‘n the wood is different 
from that in the bark. They are much smaller. There is the 
same lining of epithelium, surrounded in this case by one layer 
of thin-walled cells, which come in contact with the tracheides, 
the layers of the thick-walled cells being wanting. 
Comparing the resin passages in the leaves of the two species 
