91 
I hope that the presentation of this subject at the present time 
may direct attention to these trees and that additional observa- 
tions may be placed on record. 
EXPLANATION OF PLATE LVII. 
Fi 
Fi 
g. 1. Normal leaf of Populus grandidentata. 
g. 2. Young sapling leaf of the same species. 
Duct Formation in Chestnut Wood. 
By P. H. DUDLEY. 
The large ducts in the inner portion of each annual ring of 
Chestnut wood are very conspicuous, attracting attention at once 
in the tranverse and radial sections. When cut slightly obliquely 
inthe tangential section they form the beautiful and attractive 
contrast to the ordinary wood-cells which has long made the 
second growth of this wood so desirable for the interior finishing 
of cars, and, more recently, of houses. The large ducts form in 
one, two, and sometimes three quite distinct concentric rows 
in the early spring growth of each annual ring. The rings are 
not always alike in the same tree, owing to varying conditions of 
growth in different seasons, and marked variations are found in 
trees from different localities. Some of the ducts appear as soon 
as the wood-cells, being formed adjacent to the cells of the pre- 
ceding year’s growth, while others have only from one to three 
rows of cells between. In a specimen cut on May Ist, one row 
of ducts and eighteen rows of wood-cells had already formed. 
The leaves of this tree were only about one inch long and one- 
fourth of an inch wide, yet some of the ducts were of full size, 
well formed, having septa and well defined walls. In certain 
sections were found ducts evidently forming ; they were small, but 
with distinct walls. Around these the wood-cells were of the 
usual shape and not much flattened, and the medullary rays not 
much bent out of their course. After comparing a number of 
more or less advanced ducts, it now seems to me that they in- 
crease in size by expansion instead of by absorbing the surround- 
ing cells. If the formation of these ducts were a process of ab- 
sorption, some of the medullary rays should end at the ducts, 
and not be flattened around them, as I have found to be the case 
in all specimens so far examined. In the section before mentioned 
