NortaH Haven SAND PLAINS 609 
four points in young root. The cortex is made up of large 
cells circular in cross-section and with many intercellular spaces 
towards the periphery ; near the central cylinder the cells are ob- 
long and the tissue much denser. Most of the cells are closely 
packed with starch. 
Diameter of root, 1.2 mm. 
a ** central cylinder, .32 mm. 
tf *« largest vessels, «7B. 
TRICHOSTEMA DICHOTOMUM. — Very small root shows that the 
bundle began as a diarch, with endodermis composed of thin- 
walled cells rectangular in transverse section. The cortex cells 
are thin-walled, colorless and very large. Roots that have under- 
gone secondary thickening have many large vessels with pitted 
walls. In the sections studied there were from forty-five to fifty 
of these vessels that were distinctly larger than the other xylem 
cells. Structure of root shown on f/. 28, 6. 
Diameter of root, 9 mm. 
‘< __ central cylinder, .65 mm, 
‘* © largest vessels, 60 pb. 
VerBAscuM THApsus, —Small root has a number of small 
vessels in the center surrounded by phloem. Endodermis prom- 
_ inent, cells oblong in transverse section. Cortex is made up of 
very large thin-walled cells. Older root has a large central cyl- 
inder, containing many pitted vessels of rather small size. The 
endodermis can still be made out in some sections. The cortex 
now consists of several layers of small cells which are oblong in 
cross-section, and nearly free from starch. 
.13 mm. 
.5 mm. 
Diameter of root, 
‘6 ‘* central cylinder, 
“6 sé largest vessel, 5 a 
Linarta Lryaria.— Small root shows phloem surrounding 
ie xylem: Endodermis present. Cortical cells are very large 
and mostly colorless, but a few are filled with brown granules. 
Secondarily thickened roots have several large vessels with meas- 
urements as follows: 
.72 mm. 
5 mm. 
Diameter of root, 
od ‘* central cylinder, 
‘¢ «© largest vessels, 36 M. 
