31 
of B. papyrifera except on the young twigs peels off in thin lay- 
ers. Then we chase up the bark in the other species and find that 
it peels up tardily in thin sheets. What difference there is between 
layers and sheets Britton does not state ncr does any one else . 
know. If there is no differenc then there is no use in giving it. 
We find that the bark of B. populifolia is very white and smooth 
hut we are not informed whether it is white or black, smooth or 
in B. populifolia are deltoid, in B. papyrifera ovate, which is the 
_ proper way to put it. In B. populifolia they are pubescent on the 
veins when young, nearly glabrous when old, minutely glandular, 
leaves are long-acuminate, sharply dentate, and commonly some- 
what lobed (which statement his figure of the leaves beties), ob- 
at base. Now by a process of digestion and assimilation we 
that B. populifolia has long-acuminate leaves and B. papyrifera 
- acuminate leaves, nothing said about how long or how short- 
acuminate, B. populifolia has sharply dentate leaves and B. papy- 
_ rifera dentate leaves, nothing said about how sharp or how bluntly 
dentate. By referring to’the figures which are always excellent 
and by far the best thing in Britton’s Flora we find that B. popu- 
_ lifolia has coarsely, and obtusely dentate leaves, wnile B. papyri- 
fera has very obscurely and acutely dentate leaves. B. papyrifera 
"variable base than the other. We find that both species have 
_ slender petioles, a character that belo 
