1907] HOLM—RUBIACEAE 183 
cambium is thin-walled and continuous, with beginning cell division. 
Secondary formations have already commenced in the stele, where 
the primitive structure is no longer observable. A thick-walled con- 
junctive tissue occupies the greater portion of the central cylinder. 
Some of these secondary roots were quite thick, and were evidently 
two years old. The cortical parenchyma was thick-walled and con- 
sisted of ten compact strata, surrounding a very broad stele, in which 
the hadromatic rays were considerably longer than in the other roots. 
The capillary, lateral roots are also without hairs, and they show 
the same structure as the mother root, the only differences being that 
the cortex is smaller and that they do not increase in thickness. 
The stem.—The internodes above ground show the same structure 
as G. circaezans, but the wings are not so sharp (fig. 35); the col- 
lenchyma thus represents a broader group. In the basal internodes 
that winter over, the collenchyma is much reduced (jig. 36), while 
the cortex is frequently more or less thick-walled 
The leaves.—There is only one point in regard to the internal 
leaf-structure in which this species differs from G. circaezans, namely 
the resiniferous cells in the epidermis. These are much more numer- 
ous and often occur several together, and viewed en jace they show 
branches very often, so as to acquire a very irregular outline, instead 
of being merely oblong. Over these cells the cuticle is prominently 
striate, as observed in G. pilosum. The only characteristic feature 
by which this species may be distinguished from the others, therefore, 
depends upon the abundance and much larger lumen of the secre- 
tory cells in the leaves. 
SUMMARY 
pee to VESQUE,*? the characteristics of the Rubiaceae are 
the simple hairs; the absence of glandular hairs; the stomata accom- 
panied by at least one pair of subsidiary cells parallel with the stoma ;*° 
the crystals simple, druids, raphides, or as crystalline sand; the 
absence of laticiferous ducts. The peculiar glandular hairs which I 
found in Mitchella and Houstonia are not glandular hairs in the 
17 Caracttres des ——— familles gamopétales tirés de l’anatomie de la 
feuille. Ann. Sci. Nat. Bot. VII. 1:192. 1885. 
*8 In accordance with WarMING the stomata of Diodia radicans Cham. et Sch 
from the sandy shore of St. Thomas, have no subsidiary cells. Halofyt-Studier, p. a 
