No. 467] STUDY OF THE SALICACEE. 803 
a view which is justified not only by the reduction in size and 

IG. 2.— Salix uva-ursi. 
Tangential sections of 
tracheids with bor- 
dered pi 
wood cells. 
(Figs: 2, @,- a). 
and usually a 
length (Fig. 2, c), there is a strong tendency 
to a multiseriate ar 
fully expressed in the completely developed 
vessel as shown in Fig. 5. 
cheids, there is conside 
tribution of the bordered pits. 
many instances of pits on both the 
tangential walls (Fig. 3), 
to the vessels as shown in Fig. 5, 
will be noted that when such a vess 
upon a fibrous wood cell, 
number of the scalariform markings, but by 
the irregular manner in which such reduc- 
tion proceeds, so that the pits often lack that 
regular and definite disposition so character- 
istic of the bordered pits; and finally it is 
justified by the fact as shown in Fig. 1, that 
the scalariform markings are often wanting 
on the radial walls while characteristically 
developed on the tangential walls. 
The earliest secondary xylem is character- 
ized by the presence of true fibrous tracheids 
distinguished by the presence of bordered 
pits. These tracheids as shown in Figs. 2 
and 3, are all tapering or of the fibrous and 
fusiform type, and they vary very much in 
length and breadth. In those 
of the most slender form, 
there is but a single row of 
bordered pits which diminish 
very greatly in size as the end 


La 

: uo 
of the tracheid is approached iE 
With an increase in breadth mS 
1 
corresponding diminution of 
® DOO 

rangement which becomes 
In such fibrous tra- 
rable variation in the dis- 
Thus we find 
radial and 
a distribution COMMON  & , Salix uva- 
although it wre. Tangential 
eb abus — Quse dum 
there are no bordered v ser 
: : n to the two. : 
pits on the radial wall commo pean regc une 
This fact is expressed in 
in the case of the fibrous t 
other ways. Thus wails, and resinous 
racheids in Fig. 2, 
