1884. ] Botany. 104I 
Specimen (1) was of a light grayish color, specimen (2) was 
k brown 
Associated with the cassiterite is tourmaline, menaccanite, 
mica, zircon and rutile, the two latter scarce. Much of the cassi- 
terite is in small grains with tourmaline. 
NICKEL FROM Nevapa.—Important deposits of nickel ore have 
been discovered in Churchill county, Nevada. Some thirteen 
veins, varying in width from ten to thirty-five inches, traverse a 
ledge of rock, the gangue separating the veins consisting of sil- 
ica, iron, lime and magnesia. As recently determined by S. B. 
Newberry’, the ore at the greatest depth (eighty feet) consists of 
nearly pure niccolite. Nearer the surface oxidation products 
appear. At the ten feet level the ore is mainly the hydrated 
arseniate, or annabergite. There is every prospect that the nickel 
mines of Nevada will eventually become a prominent source of 
supply of this valuable metal. 
VANADINITE.—Vanadinite in brilliant red and yellow hexagonal 
crystals is reported by F. H. Blake? as occurring in Pinal county, 
Arizona. Wulfenite occurs at the same locality. The vanadinite 
crystals are small and are generally simple hexagonal prisms 
whose prismatic planes are striated vertically, the opposite of 
what occurs in pyromorphite. Some few modifications also 
occur, 
BOTANY.’ 
STRUCTURE, DEVELOPMENT AND DISTRIBUTION OF STOMATA IN 
UISETUM ARVENSE.‘—The stomata develop less rapidly on the 
stem than on the leaves, and hence in order to study them in 
their earlier stages, it is best to cut a section of epidermis from a 
very young stem. 
In the earliest stages I could find, the mother-cell of the stoma 
occurred as a cell of equal rank with the others, but was divided 
into four guard cells lying side by side, their longitudinal axes 
being parallel to that of the stem (Fig. 1 a). As the ordinary 
€pidermal cells develop they grow more in length than in breadth, 
While the stomata grow equally in both directions, and crowd 
upon the surrounding cells (Figs. 1 and 3). In the meantime the 
Outer pair of guard cells arch over the inner pair (Fig. 1 4) and 
finally completely cover them (Fig. 3). When mature, the guard 
cells are loaded with silica arranged in radiating bars (Fig. 3), 
and usually the inner pair is entirely hidden ; but if a thin cross- 
14 
Bia, Fourn. Sc., 1884, 
Edited by Pror, C, E. Bessey, Ames, Io 
. ’ Wade i 
* Selected for publication from original work of students in the botanical labora- _ 
tory of the University of Michigan, 1883-84. 
