LUNDELL: THE GENUS PARATHESIS 5 
The dendroid hairs, usually appearing rather coarse with magnification of 
ten to twenty times, are variable. Some are long stalked with apical branches, 
the branches of variable lengths. Others are multibranched along the trunk of 
the hair to its base. 
The simple hairs are equally variable, some villous in nature, others soft and 
straight or stiff. The glandular are predominantly papillose, but some are longer 
and gland-tipped. 
The indument of stems and inflorescences is predominently tomentose or 
tomentulose, with hairs either stellate, dendroid or simple, or in combination. 
The looseness or compaction of the tomentum is of some diagnostic importance. 
A feature of pubescence that is notable is the bizonal distribution on the 
undersurface of the leaves. Usually extending from the costa lengthwise a third 
to half the distance to the margin is a zone of hairs which is denser than that of 
the marginal section. These are designated as costal and marginal zones. Where 
bizonal pubescence is present, the marginal zone is often glabrescent. The 
incidence of bizonal pubescence is greatest where the indument of species consists 
of closely appressed stellate hairs. 
CITATIONS AND ACKNOWLEDGMENTS 
Standard abbreviations are used in designating herbaria from which cited 
specimens were studied, as follows: 
A, Arnold Arboretum, Harvard University, Cambridge. 
BM, British Museum of Natural History, London. 
C, Botanical Museum and Herbarium, Copenhagen. 
F, Chicago Natural History Museum, Chicago. 
G, Conservatoire et Jardin botaniques, Geneva. 
GH, Gray Herbarium, Harvard University, Cambridge. 
K, Royal Botanic Garden, Kew. 
LL, Lundell Herbarium, Texas Research Foundation, Renner. 
MEXU, Herbario Nacional del Instituto de Biologia de la Universidad 
Nacional de Mexico, Mexico City. 
MO, Missouri Botanical Garden, St. Louis. 
NY, New York Botanical Garden, New York. 
P, Museum National d’Histoire Naturelle, Paris. 
S, Naturhistoriska Riksmuseum, Stockholm. 
TEX, University of Texas, Austin. 
UC, University of California, Berkeley. 
US, United States National Herbarium, Washington. 
Y, Samuel James Record Memorial Collection, School of Forestry, 
Yale University, New Haven. 
To the officials of these institutions, I am deeply indebted for their cooperation 
in making available on loan the specimens on which this study is based. In 
particular the lending by European herbaria of the types of DeCandolle, Swartz, 
Oersted, H.B.K., Hemsley, Mez, Bentham and Bullock, and of other type 
material and historical specimens, has contributed immeasurably to the com- 
pleteness of this treatment. It has been possible to examine authentic material 
of all binomials in the genus. 
