Roots of Some Rosaceous Genera. 57 
multiseriate zone may or may not be slightly pigmented, but 
there is no pigment within the cell cavities. The innermost 
compact layer and the adjoining zone of three layers seem to 
constitute a year’s ring of cork; one, two or three additional 
rings may occur outside of the above described, according to 
the size and age of the root. These differ from the youngest 
only in the larger size of the most external cell layer and of 
the intercellular spaces. In a young root there may be from 
two to three zones in which the cells of the multiseriate layers 
are oval and of about equal size. As the root grows, the 
outermost cells of the multiseriate layers increase very much 
in area, with the result that intercellular spaces of peculiar 
shape and great size are formed. The cells of each uniseriate 
layer appear to increase in number by radial division, even 
after partial Suberization has taken place. The evidence for 
this statement is, that very frequently a suberin lamella is 
found surrounding two cells, these cells being separated 
radially by only a cellulose wall with no indications of 
suberin ; while a cellulose lining continuous with the radial 
wall is found upon the tangential walls of both cells. This 
apparent division of the cells in the uniseriate layer has also 
been observed in the following species: Poterium Sanguisoréa, 
Agrimonia Eupatoria, Geum album and G. nutans. Division 
of the nucleus has not been seen, since the toughness of the 
tissues in the periderm region is so great that I have not been 
able to obtain satisfactory paraffin sections. 
Group Spireee.—The only species of this group studied 
was Spirea Filipendula. This furnishes a beautiful example 
of the annular uniseriate layer with granular pigment contents, 
alternating with multiseriate layers. All the cell walls may 
be pigmented, while relatively large quadrangular intercellular 
spaces are present. The cells of the innermost zones are 
regular and of medium size, while those composing the outer 
sloughing region are much larger and irregular (Plate X, 
Fig. 6). 
