156 BOTANICAL GAZETTE {MARCH 
conjunctive tissue is quite thick-walled, but represents only a minor 
portion of the central cylinder. 
In the capillary lateral roots of second order, in which no increase 
in thickness has taken place, there is only one tangential division of 
the phellogen and only three layers of cortex. The root is hexarch, 
six groups of leptome alternating with six rays of wide vessels, and 
with a central group of thick-walled conjunctive tissue. The develop- 
ment of a phellogen has thus taken place in these roots before the 
increase in thickness of the central cylinder has commenced. 
The formation of cork inside the exodermis seems to be a point 
of interest. In roots of dicotyledons the cork usually develops from 
the pericambium, and DEBAry? records only two cases (Clusia and 
Bignonia capreolata) in which the formation of cork takes place 
in the peripheral strata of the primary cortex, as described by VAN 
TrecHEM. A similar structure, however, has been detected in 
Artanthe pothifolia, Jasminum humile, and Ruyschia Souroubea by 
OLiviER.* Since this peculiarity in regard to the superficial develop- 
ment of cork has been obscured in Bignonia, I examined also the 
roots of Tecoma radicans and found the same structure; thus Cephal- 
anthus and Tecoma may be added as examples of this very rare 
structure of roots. 
The stem.—In the flower-bearing shoots the leaves are generally 
in whorls of three, and the internodes become obtusely triangular. 
A smooth but thick cuticle covers the small-celled epidermis, which 
is moderately thick-walled, and inside of which several (about six) 
layers of cork are to be observed. Between the phellogen and the 
cortex proper is a broad continuous zone of collenchyma, which con- 
tains much chlorophyll. The cortical parenchyma is here differen- 
tiated into two very distinct zones: a peripheral, of about nine layers 
of large cells with wide, irregular lacunae; and an inner, of about 
eight compact strata of smaller cells, interrupted here and there by 
small, isolated strands of typical stereome. Of these two zones the 
2 Vergleichende Anatomie, p. 563. 1877. 
3 Recherches sur la symétrie de structure des plantes vasculaires. Ann. Sci. Nat. 
Bot. V. 13:258. 1870. 
4 Recherches sur l’appareil tégumentaire des racines. Ann. Sci. Nat. Bot. VI. 
112124. 1880. 
