NORTH AND CENTRAL AMERICAN COMMELIXACE.E— HOLM. 181 



THE STEM ABOVE liKOUND. 



The stem is cylindric, deeply furrowed. The, smooth cuticle covers a very thickwalled 

 epidermis with stomata, but without hairs. A very thickwalled collenchyma occurs as isolated 

 groups beneath the epidermis and borders on a narrow zone of thinwalled cortical parenchyma. 

 A closed ring of rather thinwalled stereome surrounds the central cylinder in which the mestome- 

 bundles are arranged in a few bands of the same structure as described above. The pith is thin- 

 walled and does not contain starch. 



THE STEM-LEAVES. 



The ventral face "I' the blade is smooth and glabrous, while the dorsal is distinctly furrowed. 

 Stomata with one pair of subsidiary cells occur on both faces; they arc level with epidermis, 

 but the subsidiary cells were observed to be somewhat raised on the ventral face. The cuticle is 

 smooth and very distinct. Epidermis consists of large cells on both faces, and the outer walls 

 are quite thick on the dorsal, but thin on the ventral face. Two or three strata of colorless cells 

 (water-storage tissue) arc located beneath the entire ventral epidermis. A few, one or two, 

 layers of thickwalled collenchyma were observed on the leptome-side of the larger veins, but 

 separated from these by small groups of water-storage tissue; no collenchyma or stereome was 

 observed on the ventral face of the blade, but a few layers of the former occupy the margins. 

 The chlorenchynia contains much chlorophyll and represents a homogeneous tissue of oblong 

 cells, but of no palisades. A thinwalled colorless parenchyma-sheath surrounds the mestome- 

 bundles in which the leptome and hadrome are well developed in the larger of these. No 

 lacunes were observed in the leaf; thus the structure is quite compact throughout. 



Tradescantia crassifolia (Javan. 



The species is perennial with erect or ascending villous stems, simple or branched. The 

 leaves are oblong, acute, densely villous, and thick. There are about five sessile inflorescences, 

 one terminal and four axillary, remote. The roots are fusiform, very thick, and develop from 

 the basal nodes. Our specimens were dried, thus we were unable to examine the internal 

 structure, of the parts above, ground, but we succeeded in preparing some of the roots so as to 

 study their structure. 



The roots are tuberous at the middle, but rather slender toward the base and apex. Epider- 

 mis is very hairy and covers an exodermis of a single layer of thinwalled cells; no foldings were 

 observed. Inside the exodermis are five to six strata of sterei'ds, which are not very thickwalled 

 and of which the cross-walls are barely oblique. These tissues show the same structure in the 

 slender and tuberous portions of the root, but the cortex and the pith are somewhat different. 

 The cortical parenchyma consists of ten layers in the tuberous portion: the cells are thinwalled 

 with narrow intercellular spaces. The innermost four layers were tilled with starch, bordering 

 on a thinwalled endodermis. A thinwalled pericambium surrounds numerous very short rays of 

 hadrome. alternating with broad groups of leptome; the position of the proto-hadrome vessels 

 could not be ascertained. The pith occupies the larger part of the central cylinder, and consists 

 of numerous compact strata of which the peripheral, two or three, are densely filled with starch. 



If we now examine the slender portions of these roots, we notice the complete absence of 

 starch in the cortex and in the pith; moreover the pith occupies here only a small portion of the 

 central-cylinder, while the number of layers in the cortical parenchyma is the same, but the 

 lumen of the cells much smaller. The roots of this species represent, thus, a combination of two 

 types — nutritive and storage roots. 



Tradescantia pinetorwm Greene. 



(T. tuberosa Greene — non Roxb.) 



This species possesses a long, creeping rhizome with cylindrical, stretched internodes from 

 3 to 5 centimeters in length. There are roots, from one to three at each node, which are very 

 thick and hairy; they vary from oblong to fusiform at the base and are terminated by a long, 



