NORTH AND CENTRAL AMERICAN COMMELINACEiE— HOLM. 189 



Aneilema, but not so in the others. Endodermis was observed to lie. more or less thickwalled in 

 Connnelhui nudif^ra. Trad< xcantia Floridana, rosea, and Warszewicziana, but thinwalled in the 

 others. The pericambium is represented by a single layer and is thinwalled in all the species; 

 it was found to be interrupted by the proto-hadrome in Commelina nudifiora, Virginica, and 

 Tradescantia rosea. The number of hadromatic rays is, of course, very variable, and the 

 largest number (twenty-one) was observed in Weldenia. In this same genus the pith is very 

 well developed and occupies the greater portion of the central-cylinder. In the other species 

 the pith is generally very little developed. 



THE RHIZOMES. 



In Tradescantia rosea the cuticle is quite thick and wrinkled, but lather thin and smooth in 

 the others. Hypodermal strands of collenchyma were observed in Commelina hirtella, but not 

 in any of the others. The cortical parenchyma is moderately thickwalled in < 'pmm< Una I irginica 

 and Tradescantia rosea; an endodermis was only noticed in Commelina hirtetta. A continuous 

 sheath of stereome surrounds the peripheral mestome-bundles in C. hirtella, while in T. rosea 

 this tissue occurs only as a few layers on the leptome-side. The mestome-bundles of the 

 peripheral bands are collateral in contrast to some of those of the inner bands, which are very 

 irregular and more or less leptocentric in T. Warszt wicziana. The pith contains deposits of 

 starch in Commelina Virginica, hirtella and in T. Warszewicziana, but not in the others; starch 

 was. furthermore, observed in the cortex of the last species, in C. Virginica and T. rosea. 



THE STEM ABOVE O ROUND. 



Several hypodermal strata of more or less thickwalled collenchyma was observed in all the 

 species examined. The innermost layer of cortex is differentiated as an endodermis in the 

 species of Commelina and Tinantia, also in Tradescantia Floridana, but not in the others. A 

 closed sheath of stereome surrounds the mestome-bundles in the species of Commelina, Tinantia, 

 and Tradescantia, with the exception of T. Floridana and rosea. In Aneilema the stereome 

 occurs only as a few isolated strata on the leptome-side. The mestome-bundles are collateral 

 and mostly arranged in several concentric bands. Deposits of starch were found in the pith of 

 C. Virginica and dianthifolia. 



THE GREEN LEAVES. 



The leaves are dorsiventral in the species of Commelina, and in Tradescantia Warszewi- 

 cziana, besides in Wrldmia; they are almost dorsiventral in T. Virginica, but isolateral in T. 

 scopulorum, Floridana, and in Aneilema. These dorsiventral leaves are held in a horizontal 

 position. 



In T. Virginica the chlorenchyma is imperfectly developed as palisades, and in the isolateral 

 leaves the palisades are totally absent. The leaves of these Tradescantia' are also held in an 

 almost vertical position, except in T. Floridana; in this species we were unable to discover any 

 trace of palisades, but our material, having been dried and pressed, was not quite suitable for this 

 purpose, and it would seem somewhat strange if the leaves of this species, which are held in 

 horizontal position, should really be isolateral instead of dorsiventral. 



In regard to the palisade-tissue, we might state that the palisades observed in '/'. rosea were 

 not typically 7 developed. The pneumatic tissue attains its highest development in Weldenia and 

 T. Warszewicziana. where it is composed of star-shaped cells, while in the others the shape is 

 more irregular, but always with wide intercellular spaces. 



The mechanical tissue is. to some extent, well represented in the leaves. Collenchyinatic 

 strands were thus observed above and below the midvein in Commelina nudiflora, Virginica, and 

 erecta, or below this in Am ilt ma; or only on the leptome-side of the larger veins in C. hirti lla, 

 dianthifolia, T. rosea, Virginica, scopvlorum, Weldenia, and Tinantia; or in the leaf margins, as 

 in C. dianthifolia. Stereome was observed in T. Warszewicziana on the leptome-side and in the 

 margins; on the leptome-side alone in Aneilema and C. Virginica; or on both faces of the veins 

 in C. dianthifolia. 



