NORTH AND CENTRAL AMERICAN COMMELINACE.E-- HOLM. 165 



panion cells well differentiated; the hadrome consists of two reticulated and one ring-vessel. 

 Two very small mestome- strands are located in the leaf-margins, and their structure is very 

 simple (PI. V, fig. 27); the parenchyma-sheath (P). of which two cells are moderately thickened, 

 surround a group of leptome and one or seldom two reticulated vessels. 



A somewhat similar structure is to be observed in the green spathe which surrounds the 

 inflorescence. The dorsal face of this leaf is very scabrous from numerous short pointed and 

 somewhat curved hairs, accompanied by the same kind of wartlike and clavate which were 

 noticed on the stem-leaves. The epidermis is otherwise thinwalled and covers a chlorenchvma 

 of two to three strata of open pneumatic tissue, but no palisades; raphide-cells are very numer- 

 ous, but much shorter than those in the stem-leaves. No collenchyma accompanies the veins, 

 the minor structure of which agrees with that of the veins of the other leases. 



The fore-leaves are tubular and membranaceous, almost colorless. Epidermis is thinwalled 

 on both faces, and lacks the pointed hairs and the papillae, while a few clavate were observed on 

 the dorsal face. This tissue, the dorsal and ventral epidermis, is the only one of these [eaves 

 except around the nerves, where a few parenchymatic cells form an incomplete sheath; the 

 mestome-bundles, eight in all. contain mostly leptome, and are not supported by any cover of 

 collenchymatic tissue. 



Although no chlorophyll was observed in the fore-leaf, a few stomata were, nevertheless, 

 noticed, and these showed the same structure as those of the green leaves. 



Commelina Virginica L. 



The Rhizomk. 



A rhizome is developed in this species, but it is short and condensed (PI. II, fig. 8); it con- 

 sists of a few erect internodes, each of which represents the base of an erect aerial shoot with 

 usually two roots. These roots develop from the ventral face of the internodes; they are thick, 

 dark brown, and densely covered with hairs. They branch but sparingly, and the lateral ramifi- 

 cations are more slender and of a lighter color. The rhizome has no horizontal internodes, and 

 its further growth is only secured by the development of a bud in the axil of a scale-like leaf, 

 situated near the base of the short, erect internode. This bud is developed on the side of the 

 shoot, alternately to the right or left; thus the rhizome grows out in a zigzagged direction. 

 This structure of the rhizome may he more easily understood if we examine the smaller specimen 

 drawn on the same plate (fig. 10) with its diagram (tig. 11). The base of the old shoot (A) repre- 

 sents only one internode, and the leaves have faded away completely. A lateral branch has 

 pushed out (A 1 ) which bears a bicarinate foreleaf (P 1 ) and two scale-like membranaceous basal 

 leaves (L 1 and L 2 ). Of these the foreleaf turns its back towards the mother-axis (A), while the 

 two other leaves are turned ninety degrees to the side of this, alternating with each other, as 

 seen in the diagram (tig. 11). Two axillary buds (B' and B 2 ) are visible, and it is the latter of 

 these (B 2 ) which develops into an aerial shoot during the succeeding year, while the other one 

 (B 1 ) stays dormant. 



If we return now to the larger rhizome (ties. 8 and 9), we notice the same arrangement of 

 leaves and position of buds, besides that the lateral, aerial branch (A 2 ) from the axil of leaf (L 3 ) 

 does also bc<jin with an addorsed fore-leaf (P 2 ). 



It seems, thus, characteristic of the rhizome of this species that no horizontal internodes occur, 

 that the growth takes place in a zigzagged direction, and that the laid in the axil of leaf (L 1 ) remains 

 dormant. 



The Aerial Shoot. 



It is not uncommon to find specimens with a simple, erect stem terminated by an inflorescence 

 and with no indication of lateial Moral or vegetative shoots. Most frequently, however, the stem 

 is branched and often very profusely so. Lateral shoots may thus develop from the axils of 

 nearly all the stem-leaves, and these lateral shoots are again terminated by an inflorescence, besides 

 that a few, two or three, inflorescences of third order may be observed near the apex of each lateral 



