1917] FAUST—RESIN SECRETION 453 
spicuous now (fig. 10) by anticlinal suberization. The appearance 
of the thickenings is knotlike or looplike along the radial walls. 
The endodermis, unlike that of Parthenium argentatum, contains 
“no starch grains such as commonly occur in higher plants. 
The secondary xylem contains not only well defined spiral 
vessels and tracheids, but vessels of intermediate type. For 
instance, in fig. 11, ¢ and d with bifurcating spiral reinforcements 
are not far removed from a, the true spiral type, while e more 
nearly approaches the eyelet type so characteristic of the tracheids. 
In the dicotyledons the usual type of axial structure is par- 
enchymatous; but such is not the case in B. sagittata, for there the 
wood elements soon work centripetally, crowding against the origi- 
nal plate cells. The latter become sclerified, so that the plate 
becomes a solid disk of vessels and sclerome. Such sclerification 
begins before radial suberization of the endodermis and consider- 
ably earlier than resin duct formation. The centripetal crowding 
with the addition of the new xylem elements increases the actual 
size of the region within the cambial ring. 
The suberized endodermis serves a twofold purpose. The suber- 
ization thickens the walls and allows the endodermis to act as a 
. supporting girdle, and, in addition, acts as an impervious barrier 
against an external translocation of food material. Russow (17) 
has described two types of suberization of endodermis, that in 
which the radial and one tangential walls are thickened (his ““C”’ 
type), and that in which the entire wall is thickened on all sides 
(his “O” type). HABERLANDT (6, p. 372) suggests that such dis- 
tinction is not of great mechanical importance, since variations 
may occur within the same genus, such as Carex, Smilax, etc. 
Although the ‘‘C” type is the most usual in B. sagittata, there also 
occurs the “‘O”’ type, and in woody secondary roots a thickening 
which may be designated as an ““H”’ type (fig. 12). In the primary 
root of 5 mm. or over, the suberized endodermis is interrupted in 
regions between resin canals by phloem strands which cross into the 
cortex in these regions, leaving open an avenue for translocation of 
materials in these special places (fig. 13, ph). The origin and 
development of the resin canals will be discussed later in this 
paper. 
