98 Barratt . — The Origin of the 
the outer part of the plerome is that described above, and thus normally 
three layers of the inner cortex, including the endodermis, take their origin 
from the outer plerome. 
This conclusion agrees with that of Schoute, and is thus directly 
opposed to the earlier explanation given by Sanio, who considered that the 
E- ND 
Fig. 6. Transverse section through older stem, showing the formation of the endodermis and 
final appearance of air-canals, end., endodermis. 
three layers in question originated by the subdivision of the innermost layer 
of the periblem. 
Although the observations do not coincide in exact detail with those of 
Schoute, this is probably to be accounted for by the fact that, owing to this 
investigation having been confined to this one species, it was possible 
to examine a large number of apices and thus to obviate the disadvantages 
