204 
typical form, they can hardly be considered otherwise than as 
transitional between simple and bordered pores. The family 
Ericacez is also interesting on account of the difference in the size 
of borders found in its different genera. In Evica the border is ex- 
ceedingly small, in Ca//una not much larger, in Ledum and Arbutus 
a marked increase in size is seen, so in Andromeda and Rhodo- 
dendron until at last in Vaccinium and Oxycoccus the border 
reaches a medium size; that of Vaccinium, in one instance, meas- 
uring 5mm. Only in the genus Erica were starch grains present. 
In the family Apocynacez there is also considerable variation 
both in the frequency of pores and size of borders, but in the latter 
case it is much less marked than in the family Ericaceze. The 
borders of the genus Zabernemontana, where the starch grains 
were found, are, if possible, even smaller than those of Erica, but 
perfectly typical in form. 
In the majority of instances, the pores were situated on all 
sides of the cell. Exceptions to this occur in proximity to 
the limit of the year’s ring. Here they are principally on the 
tangential walls. Ina few families they show a decided prefer- 
ence to the tangential walls throughout. In Drimys the simi- 
larity between their arrangement and that of the pores of | 
conifers is very noticeable. The specimen examined was a one 
year’s stem; the pores are entirely limited to the radial walls, 
except in the last eight or ten layers next the cambium ring. 
Here they occur principally on the tangential walls. This genus 
resembles the conifers also in the size and frequency of the bor- 
ders, and in the predominance of this tracheal element. 
Of the thirty-three families containing only simple pores in 
the libriform tissue no special mention is necessary except as re- 
gards one point. Whatever may be the functional differences in 
the elements of the woody tissue, the extreme contrast between 
the most complex and simple forms suggests some plan for the — 
division of labor in the more complex. If, as some authors 
have suggested, the office of the trachez is to supply the need of 
water in the leaves, caused by transpiration, while that of the 
tracheids is to supply the local demands, which exist in all living 
parts of the stem, it might be inferred, that in those cases where 
the libriform has only simple pores, there would be found thin- 
walled tracheids, artd in cases where the libriform was liberally 
supplied with bordered pores, the other tracheal element would 
not be apt to occur in such large quantities, 
: (To be continued.) 
