16 BOTANICAL GAZETTE | JANUARY 
spontaneously were rejected. Further details in the treatment 
of the roots will be given in connection with the different 
experiments. 
It will be necessary to understand the general anatomy of 
the root in the zone of growth. At the extreme tip of the root 
is a very well developed root cap which extends back as a 
sheath surrounding the whole root for 5™™ or more. Where the 
cap joins the tip of the root proper is the zone of initial cells or 
primary meristem. From this meristem are derived by cell 
division all the cells of both the cap an. root proper. All the 
cells of the initial zone are completely filled with dense granular 
protoplasm. A very short distance above the initial zone, 1™ 
or more, may be distinguished a central or axial cylinder com- 
‘posing, approximately, one third of the diameter of the root; 
and this central strand is surrounded by a cylinder of cortical 
_ parenchyma, characterized by numerous large intercellular 
spaces. These spaces are more conspicuous in the longitudinal 
than in the transverse direction, and may be followed very near 
to the initial zone. In sections of living roots these spaces are 
shown by the presence of air. Outside of the cortical parenchyma 
is the dermatogen layer, one or more cells thick. The cells of 
the dermatogen layer are more densely filled with protoplasm 
than the cortical layer, whose cells have a comparatively small 
amount of protoplasm, and a very large central vacuole. The 
cortical cells often have a large amount of starch in them. The 
outer layers of the axial cylinder are also densely filled with 
protoplasm and furnish the path along which the reserve food 
is brought from the cotyledons to the growing cells, as has been 
determined by experiment. 
The cells of the initial zone are nearly isodiametric. The 
portions of the cortex nearest the initial zone often have the 
radial diameter of cells longer than the diameter parallel to the 
root axis. ; 
. Finally,all the cells come to have their longer diameter parallel 
to the long axis of the root. The cells of the axial cylinder 
elongate longitudinally much earlier than the cells of the cortex. 
