804 
THE AMERICAN NATURALIST. (VoL. XXXIX. 
it will be seen that the pits are confined chiefly to the tangen- 
pitted tracheid. 
X 350. 

tial walls, and appear on the radial walls at the 
ends only of the tracheids (Figs. 2, a, c), or they 
may even be completely eliminated from the radial 
walls as in Fig. 2, 4. Such variations are also to 
be seen in Fig. 4. One variation of such relations 
worthy of note, was found in radial section. A spi- 
ral tracheid of the protoxylem was immediately fol- 
lowed on its outer side, by a fibrous tracheid with 
round, variably distant bordered pits in one series. 
The tangential wall common to the two was also 
provided with a continuous series of bordered pits. 
Immediately outside the fibrous tra- 
cheid, and therefore on the side oppo- 
site the spiral tracheid, was a fibrous 
wood cell presenting no pits of any 
kind upon either its radial or its tan- 
gential walls. The illustrations thus - 
given in detail, serve to illustrate the 
general fact that all sorts of transi- 
tional forms are to be found, con- 
necting the fibrous elements of the 
secondary xylem with the cylindrical 
and more or less tubular elements of 
the protoxylem ; and it is quite evi- 
ent that we have in Safir uva-ursi 
the same sort of a transition zone as 
D Boe >> 
OOO 
OLG 
X 
© 
DD 
G) 
OION 
d 
SS 
RS 
E > 
v (ct 
1G, 
RUN 
© 
(2) 

that which has already been shown to exist in the 
gymnosperms (Penhallow, :00), the two cases dif- 
fering chiefly with respect to (1) the radial extent 
of the zone, (2) the number and extent of the tran- 
sition. forms, and (3) the specific character of the 
final products. When we consider the various 
transformation stages occurring in Salix uva-ursi, 
the peculiar conditions of reduction in the struc- 
tural details of the cell wall, the special alterations 
in the form of the individual elements, and the 
cells, the muiti- 
seriate bordered 
pits on both ra- 
ty 
brous tracheid. 
x 
peculiar association of these derived forms, it is exceedingly 
