1907] HOLM—RUBIACEAE 157 
peripheral contains chlorophyll, besides calcium-oxalate in the shape 
of crystalline sand. Inside the cortex is the central cylinder, consist- 
ing of a broad zone of leptome, some strata of cambium, and many 
rows of vessels separated by narrow medullary rays. The central 
portion of the internode is occupied by a thin-walled but solid pith, 
in which crystalline sand was noticed. 
A somewhat modified structure is to be observed in the shoots of 
younger specimens, which are yet purely vegetative. In these the 
leaves are opposite, not whorled in threes as in the floral shoots, and 
the outline of the internodes is cylindric. The cuticle is wrinkled, 
and no phellogen is developed; thus the collenchyma borders directly 
on epidermis. The differentiation of the cortex into two zones is not 
so distinct, since the parenchyma is more uniformly developed, more 
compact, and with the cells radially arranged from the periphery to 
the stele, except where it is interrupted by the stereome, which occurs 
in very small, scattered groups. There is no endodermis, and the 
structure of the mestome and pith is identical with that of the floral 
shoots. 
In comparing these internodes of floral and vegetative shoots with 
the slender peduncle that bears the globose inflorescence, it is inter- 
esting to notice that the structure is almost identical, with the excep- 
tion that the number of strata of the various tissues is smaller, that 
no cork is developed, and that bicellular pointed hairs abound. 
The leaf.—The blade shows a bifacial structure. The cuticle is 
somewhat irregularly thickened so as to form striations, especially 
lengthwise (parallel with the midrib). Very characteristic is the 
small-celled epidermis with the radial walls straight on both faces of 
the blade; the stomata, which are confined to the lower face, have 
mostly two subsidiary cells parallel with the stoma (jig. 2), but varia- 
tions are frequent, there being sometimes two subsidiary cells on one 
side of the stoma and only one on the other, or the differentiation of 
the epidermal cells surrounding the stoma may be so slight that no 
typical subsidiary cells are observable. The stomata are level with 
epidermis and the air chamber is quite wide and deep. While the 
upper surface of the blade is glabrous, the lower is hairy with uni- 
and bicellular hairs, which are long, more or less curved, with the 
apex acute, thick-walled, and covered by a striately thickened cuticle. 
