832 Journal of Agricultural Research voi. xxvii, no. i» 
Burbank. —Periderm very wide and covered with a rough and jagged- 
crust in the Russet types.. Thickness of periderm layer is 156-169- 
microns; average number of rows 7-11. The cells show a fairly regular 
arrangement in radial rows; the width of the rows, however, varies 
greatly. The mcst common type of cell measures 78 by 18.2 microns. 
Fig. 8.—Semidiagrammatic drawings of periderm of potato tubers. X40. 
Transition to the cortex is effected by four rows of small periderm-like 
cells (PI. 10, I, J, and fig. 7). ^ 
Green Mountain. —Periderm thin or of medium thickness, covered 
with thin rough crust. Layer measures 104-125 microns, occasionally 
more. Number of rows seven to nine. The cells are uniform and show 4 
