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 Sanguisorba, 

 Agriinonia Eupatoria, Gcuin album and G. tmtans. 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 Spirceea. — The only species of this group studied 

 was Spircea 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). 



