454 BOTANICAL GAZETTE [DECEMBER 
In the older rootstocks of two or more years’ growth three 
regions may be distinguished, a basal primary root, a median 
swollen region, and two or more branched root growths above the 
swelling. From the upper reaches of these proximal root branches 
arise the aerial portions of the plant system. The lowest root 
region is characterized by a single row of resin canals and an axial 
- stele, while both of the other parts have two concentric rows of 
resin canals (fig. 14). Cross rays connect these longitudinal canals 
at frequent intervals. These old rootstocks are further character- 
ized by lysigenous splitting of the now functionless rays, so that the 
wood is split apart in almost every ray region (fig. 15, /:, 1,). This 
cracking is probably caused by tension in the wood areas and a 
shrinking of the cells in the near vicinity. 
The subsidiary root system of B. sagittata varies from the main 
system in that it is diarch in type. The protoxylem first becomes 
differentiated as two groups at opposite poles, with evidence of 
protophloem developing intermediately (fig. 16). By the time the 
suberization of the endodermis occurs, intermediate wood elements 
have developed and the axial plate is well sclerified (fig. 17). It 
is not until considerably later that the resin ducts arise (fig. 18). 
The root of the plant has a rather large wood area compared with 
the extra-cambial portion of the root. Table IV shows that it is 
practically a ratio of two to one through all stages of secondary 
thickening. 
TABLE IV 
Number Diameter of root Ratio 
Risk ke we w he aes | mm. pe 
BoP gin so, ware 2 °§ 2° 
Boncy ae ees 4.5 art 
Bee: ease 12 8:5 
ae ogre ata a! 12 at 
This excess of wood tissue may be accounted for by the area 
occupied by the rays extending between the wood elements. In 
no. 5, with two rows of resin canals, lysigenous cracks in the ray 
region occupy about half of the wood area. 
While the tracheids conform to the usual type for Compositae 
and the phloem cells show no unusual ‘characteristics, certain 
