Angewandte Botanik, 61 



The leafstructure is bifacial; roundish papillae from epidermis are 

 frequent on the dorsal face. A Single Stratum of rather low palisa- 

 des Covers an open pneumatic tissue. While the midrib is composed 

 of only a Single open mestome-strand, the petiole con- tains ten 

 separate mestome-bundles arranged in a circular band. 



Theo Holm. 



Holm, T., Medicinal plants of North America. 7 9. Dioscorea 

 villosa L. (Merck's Report. XXII. p. 311-314. f. 1—30. New York, 

 Dec. 1913.) 



The rhizome of Dioscorea villosa L. contains saponin in abun- 

 dance, while the so-called "dioscorein" is said not to be a definite 

 principle, but simpl}^ a dried solid extract, according to C. G. Lloyd. 

 The plant is described and figured. and much attention is given to 

 the seedling and the anatomical structure. In respect to the seedling- 

 stage the cotyledon has an orbicular blade, but remains enclosed 

 within the seed; the membranaceous sheath surrounds the plumule, 

 of which only a Single, long-petioled, green leaf appears during the 

 lirst season; the primary root is short. Late in the fall the green leaf 

 withers, but at that time the plumule has grown out and developed 

 a horizontal tuber of a few internodes; in some cases a small tuber 

 had become developed from the axil of the green leaf. While the 

 primary root soon ceases to be active some few secondary roots 

 become developed from the basal part of the tuber. At the age of 

 three years the young plant shows generally a short stem of a 

 Single, aerial internode with two green leaves, and it takes several 

 years before the plant reaches maturity and produces flowers. In 

 regard to the internal structure the foUowing points may be men- 

 tioned. A heterogeneous cortical parenchyma was observed in the 

 secondary roots viz. the peripheral strata being thinwalled, and 

 more or less broken down so as to form wide lacunae, while the 

 innermost layer is thickwalled, some of the cells showing spiral 

 thickenings. The pericambium consists of several strata, very thick- 

 walled outside the leptome, but thinwalled outside the hadrorae. 

 Although no stereome is developed the rhizome is of a very firm 

 structure, due to the compact parenchyma filled with starch. No 

 endodermis and no pericycle was observed in the rhizome, the 

 mestome-strands being scattered throughout the parenchyma; they 

 are either coUateral, or contain only leptome. The stem above 

 ground has a few layers of collenchyma surrounding a narrow zone 

 of cortical parenchyma, and there is a distinct endodermis, inside 

 of which foUows a closed sheath of stereome. In respect to the stele 

 there are two almost concentric bands of mestome-bundles, of which 

 the peripheral have the leptome more or less embedded in stereome, 

 while in the interior band the leptome is free. Characteristic ofthe 

 mestome-strands is the occurrence of two leptome-groups, the one 

 located outside the hadrome, the other one between the vessels. 

 The leaf is bifacial, with a typical palisade-tissue of high cells 

 covering an open pneumatic tissue. No endodermis surrounds the 

 midvein, but there is a closed sheath of stereome in which several, 

 small Strands of leptome are embedded. In the petiole are eight 

 mestome-strands, each with an endodermis and an arch of stereome 

 on the leptome-side. Theo Holm. 



Holm, T.. Medicinal plants of North America. 8 0. Verbas- 



