June, 1907.] 
Ohio Plants with Punctate Glands. 
179 
have practically the same structure as the light glands, but are 
made dark by the secretion which is contained in them. The 
age of the leaf may also have some influence on the darkness of 
the spot. 
The glands of Boebera papposa (Fig. 4) appear to the naked 
eye as large yellow spots, oval in shape. The gland wall is very 
thick being made up of a number of layers of cells like the 
prickly ash. The cells composing the wall stain quite dark on 
the outside, but the inner layers take the stain much less prom¬ 
inently. The cells in the innermost layer are irregular in shape 
and remain very light in color. They are sharply limited from 
the adjoining layer by a definite heavy wall. The gland is a 
little less than twice as long as broad, and extends from the upper 
epidermal layer to the lower epidermis. 
The internal glands of this type usually secret volatile oils, 
but the glandular peltate scales found on the surface of the 
leaves and stems very commonly secret resin, although no ab¬ 
solute distinction can be made. Gaylussacia resinosa (Fig. 8) 
is provided with external scales on the under side of the leaf. 
These scales are attached to the leaf by stalks which are made up 
of about seven cells. The scale itself is divided into from six to 
ten cells. The resin is secreted from this and as the scale becomes 
mature the outer covering is pushed off by the secretion. This 
produces a bulging out of the scale, and the whole structure is 
surrounded by a mass of bright yellow resin. The illustration 
shown in most texts of this type is the gland found on the bracts 
of the common hop Humulus lupulus, but the hop gland is more 
simple in structure. The cross-section of the leaf of Gaylus¬ 
sacia shows no further adaptation for secretion, and even the 
lower epidermal covering is perefctly normal. The longitudinal 
section shown (Fig. 9) is cut through the base of the disc and 
therefore show r s one central cell of the stalk and eight surrounding 
cells of the scale proper. These cells show rather large dark 
nuclei and contain abundant cytoplasm. 
In Glecoma hederacea, common ground ivy, (Fig. 7), resin 
is also secreted, but the position of the scale is somewhat differ¬ 
ent. Instead of secreting scales on the surface of the epidermis, 
the organs for this purpose are in depressions or pits. The 
gland has a stalk of two cells and below a scale showing a row 
of from three to six cells in cross-section. These cells stain quite 
dark but the nuclei can be seen without difficulty. The outer 
wall of the scale is separated from the protoplasm of the cells 
by a definitely limited clear space. 
Besides the glandular tissue on the inside and glandular 
scales, other glandular structures are developed from the epi¬ 
dermis which represent true epidermal hairs or emergences. 
The hairs may be of different types, unicellular or multicellular. 
