242 BOTANICAL GAZETTE. [ October, 
are presently encroached upon and obliterated by the devel-. — 
opment of contiguous cells, thus forming a continuous oily 
layer composed of obliterated ducts and intervening secret- 
ing cells. In Conium no ducts are developed, because groups 
of cells are not set apart as secreting cells, but only a single 
layer of cells, and there can thus be no development of inter- 
cellular spaces, although the power of radial division is re- 
tained. Hence Hydrocotyle has no oil-ducts because its 
secreting cells lack the power of radial division; Conium 
has none because its secreting cells are in a plane instead of 
in groups; while most Umbellifers have oil-ducts because 
the undifferentiated parenchyma into isolated patches, 
also being very thick-walled. In certain genera the strengtl 
éning-cell groups of the mature fruit are in the same condl= 
‘on as those of Cherophyllum at anthesis, viz.: differing 
from the surrounding parenchyma only in smaller size, and 
