VOL. XI, NO. 12 .- BOTANICAL GAZETTE .- DEC., 1886.

The Bulliform or Hygroscopic Cells of Grasses and Sedges compared.*

W. J. BEAL.

( WITH PLATE X.)

As so little attention has been given to this topic, it will be necessary first to describe briefly the leaf of a grass. In general, it
consists of a sheath encircling the stem, and a lamina spreading
from the upper part of the sheath. The blade is traversed longitudinally by fibro-vascular bundles which vary much in size and
degree of perfection. In viewing a magnified transverse section
of a mature leaf of Sesleria (fig. 1), we see: e, an outer envelope
of cells, the epidermis; b, the median fibro-vascular bundle; h, h,
lateral bundles ; a, the lower median strand of hypodermal fibers;
d, the upper median strand ; c, d', the lateral strands. The other
cells are parenchymatous, most of them containing granules of
chlorophyll. The vacancy, i, is the lacuna, caused by the rupture
of some cells. In aquatic grasses the lacuna are very large.
The epidermal system consists of: a, epidermis proper ; f, g, bulliform (blister) cells; c, stomata ; d, trichomes.
Of the bulliform cells I speak more particularly. They are
in longitudinal parallel lines, are larger, extend further into the
leaf, and have thinner walls than ordinary epidermal cells. They
are usually more or less wedge-shaped, with the point of the
wedge towards the outside of the leaf. When dry, these cells
contract and aid in closing the leaf in two or three ways; when
moist the leaf expands again. In Zea Mays (fig. 2) these cells are
raised above the others and puff out like a blister. When viewed
on the surface of the leaf the bulliform cells are usually seen to
have the proportions of length and width much like those next
to them.
The number of rows in a species appears to be always uniform, but the number varies with the species from three to twelve
in a band. If there are many rows the cells are shallow; if few,
the cells are deep; if three only, those at the side are small, and
the middle one is very large. The arrangement or plan of these
cells is quite constant in a species, but in a genus they often vary
widely.
The following examples will give some notion of the variety,
the sections being made in the widest part of the leaf:

*Read before the A. A. A. S. Buffalo meeting, 1886.

1. The leaves of Dactylis glomerata have one median band (fig. 3).
2. In Chloris petræa there is one middle band, and one or more on each side.  
3. The leaves of Poa pratensis have two bands, one on each side of the middle (fig. 4).
4. Andropogon squarrosus has one band each side of the
middle and a small one at each edge.
5. The leaf of Phleum pratense has one band of several shallow cells each side of the middle and others between the veins
(fig. 5).
6. The leaves of Zea Mays have a band between each two
primary bundles and above each third class bundle (fig. 2.)

Fig. 10.

7. The leaf of Leersia oryzoides has numerous bands on the
upper surface each side of the middle, and one band each side of
the keel on the lower side (fig. 6).
8. The leaf of Amphicarpum Purshii has opposite bands of
bulliform cells on both surfaces, though those above are most
prominent (fig. 7).
9. In case of the leaves of Panicum plicatum the bands of
bulliform cells are first on the upper side and then on the lower,
and are found in grooves (fig. 8).
10. The leaf of Andropogon prinoides has large epidermal
cells of nearly uniform size distributed all along the surface,
excepting over the veins (fig. 9).
11. The leaf of Paspalum plicatum has a very irregular epidermis, with groups of cells in the center of the leaf, several
above each other, as well as side by side, all acting as bulliform
cells (fig. 10, text).
In vernation the leaves take the same positions as when full
grown and dried, though the bulliform cells at that time are very


small. The leaves of Dactylis and Poa pratensis are conduplicate
when slowly dried, while those of Phleum are convolute. The
leaves of Panicum plicatum, when dry, close in a zigzag manner
like a fan. The object accomplished by the closing or rolling of
the leaves is to cover one surface and assist in preventing excessive
evaporation in dry weather.
The examples here cited belong to various genera and tribes
of grasses, and give a fair idea of the varied forms of bulliform
cells, though these are by no means all the varieties that might be
shown.
In a similar manner let us now glance at some of our common
species of Cyperaceæ, and compare them with some leaves of
grasses.
1. The leaf of Cyperus rotundus, var. Hydra, is narrow and
thin, having a single deep band of bulliform cells above the
midvein (fig. 11). The epidermal cells are rather large and nearly
uniform in size. The bulliform cells are much like those of
Dactylis glomerata. The epidermal cells on the upper side are
much larger.
2. In case of Kyllingia pumila the upper epidermis occupies
nearly half the thickness of the leaf, the cells above the midvein
being scarcely larger than those on either side (fig. 12). This leaf
may be compared with Andropogon prinoides, though in the
latter case the epidermal cells over the veins are small.
3. The leaves of Heleocharis, so far as seen, have leaf-
blades which are very small or rudimentary.
4. The leaves of Scirpus sylvestris are wide, with many
veins, opposite each one of which, above and below, there is a
depression. There is one band of about eight cells above the
midvein and these have only a moderate depth. The epidermal
cells are rather small and can scarcely act as bulliform cells.
The leaf much resembles that of Dactylis glomerata, but the bulliform cells are not so deep.
5. The blades of Scirpus validus, the great bulrush, are very
short, almost rudimentary. The lacunæ are large and near the
upper surface of the leaf. The cells of the upper epidermis, as well
as several layers below, are rather small, thin-walled, not varying
much in size. All of these small cells act as bulliform cells and
the leaf becomes convolute or involute when drying.
6. The leaves of Fimbristylis autumnalis (fig. 13) have a
thick epidermis of one layer of thin-walled cells, which extend
nearly to the lower side of the leaf. This much resembles the
leaf of Andropogon prinoides, though in the latter the cells over
the veins are small.

7. On examining a leaf of Eriophorum Virginicum we see
that it is very thick, with many veins and lacunae. The epidermis is composed of small cells; the single band of bulliform cells
over the midvein consists of about eight rows of considerable
depth. The epidermal and bulliform cells are much like those of
Daetylis glomerata.
8. In Fuirena squarrosa the cells of the upper epidermis
extend about one-third the depth of the leaf and are somewhat
uniform in size. There is no special enlargement of these cells
above the midvein. The epidermis is much like that of Fimbristylis autumnalis and Kyllingia pumila among sedges, and
Andropogon prinoides among grasses, except the cells above the
leading veins are as large as any, while in the grass they are very
small over the veins.
So far the examples of leaves of sedges noticed belong to one
tribe, Scirpeæ.
9. The leaves of Rhynchospora capillacea (fig. 14) are very
narrow, with a few veins, small epidermal cells, and a band of
bulliform cells reaching more than half way across and extending
nearly one-third the depth of the leaf. This may be compared
to a very narrow leaf or the apex of a leaf of Dactylis.
10. The leaf of Cladium mariscoides is rather thick, becoming thinner at the margins and toward the midvein. The epidermal cells are small and have thin walls; there are many layers
of similar thin-walled parenchyma cells below the epidermis;
but no distinct band of bulliform cells. The leaf reminds us
very much of the leaf-blade of Scirpus validus.
The last two examples belong to the Rhynchosporeæ.
11. The bulliform cells of Seleria triglomerata are much like
those of Carex vulpinoidea (fig. 15).
The following eight examples are selected from the large and
difficult genus Carex :
12. The blade of C. vulpinoidea (fig. 15) is of medium thick-
ness, having about six bulliform cells extending one-third the
way to the lower side of the broad shallow midvein. Between
the veins there is a noticeable enlargement of about six epidermal cells, the other epidermal cells being rather large. These
side bands approach in appearance the side bands in Phleum
pratense, only they are less distinct.
13. C. lagopodioides has a leaf much resembling the last,
but the epidermal cells do not show a resemblance to bulliform
cells.
14. C. Grayii is a coarse species found in low and wet places.
The epidermal cells are of moderate size; the lacunæ are large.

There is one band of bulliform cells of about twelve rows, extending one-half the depth of the leaf, if the deep narrow midvein
is not taken into account. So far as bulliform cells are concerned
this reminds us of a leaf of Dactylis glomerata.
15. C. Pennsylvanica is an early upland sedge with narrow
leaves. The epidermis (fig. 16) is composed of small cells. There
are six rows in each bulliform band, and these extend about
two-fifths of the way down to the lower side of the midvein.
The epidermal and bulliform cells remind us again of a leaf of
Dactylis glomerata.
16. The blade of C. utriculata is very thick, narrowing to
the margin and in the center. The epidermal cells are of moderate size; the single band of bulliform cells number about ten
and are over the midvein. This leaf reminds us very much of
that of Eriophorum Virginicum, but in the former the vessels of
the fibro-vascular bundles are near the upper surface, while in the
latter they are near the lower side.
17. In the wide coarse leaf of C. Careyana (fig. 17) the
upper epidermal cells are rather prominent, varying considerably
in size. There is one very wide band of about twenty bulliform
cells over the midvein. In the center of the leaf they extend two-
fifths of the distance to the base of the vein. About half way
from the midvein to the margin of each side of the blade there is
a longitudinal crest or ridge on the upper side. The prominent
vein at this place has small epidermal cells and hypodermal fibers.
On the upper surface on either side of this vein and ridge the
epidermal cells resemble a wide shallow band of bulliform cells.
18. The leaf of C. Hitchcockiana is much like the last one
named, and there are many leaves of Carex proper of like
structure.
19. The leaf of C. laxiflora, var. latifolia (fig. 18) is about an
inch wide and rather thin. The epidermal cells are somewhat
prominent. There is one band in the middle of about ten bulliform cells, which cause this wide leaf to he conduplicate when dry.
In the leaves of Carex the pitted vessels of the fibro-vascular
bundles are near the lower side of the leaf.
It will be seen that all the leaves of sedges have been com-
pared with some one of five genera of grasses. In the sedges, so
far as studied (many genera of four tribes), I find nothing in the
middle of the leaf to compare with that of Poa pratensis, Phleum
pratense, Leersia oryzoides, Amphicarpum Purshii, or Panicum
plicatum. The bulliform cells and other epidermal cells, the
hypodermal fibres, and the lacunae vary more in grasses than in
sedges, or in other words, we find a greater variety of forms of

these cells or groups of cells in grasses than in sedges. Perhaps
we should expect this as most of the sedges thrive in wet places,
where the conditions are uniform, while the grasses thrive in a
much greater variety of places. Still we find a greater differentiation of parts in the leaves of marsh grasses than in the sedges
growing near them.
Some of these characters in the leaves of grasses and sedges
may be useful in description and classification.
EXPLANATION OF PLATE X .- The drawings are all diagrammatic and represent portions of the transverse sections of the leaf. Fig. 1, Sesleria cærulea;
a, median strand of hypodermal fibres; b, median fibro-vascular bundle ; c d',
lateral strands of hypodermal fibres; e, epidermis ; f, bulliform cells when leaf
is closed ; g, same when leaf is open; h h, lateral fibro-vascular bundles;
i, lacuna, X120 (Douval-Jouvé). Fig. 2, Zea Mays, X17 (Sudworth, in Beal's.
Grasses). Fig, 3, Dactylis glomerata, X38 (Sudworth, l. c). Fig. 4, Poa pratensis, X75 (Sudworth, l.c). Fig. 5, Phleum pratense,X20 (Sudworth, l. c).
Fig. 6, Leersia oryzoides, X350 (Douval Jouve). Fig. 7, Amphicarpum
Purshii, X25 (Sudworth, 1. c). Fig. 8, Panicum plicatum, X10 (Douval --Jouvé). Fig. 9, Andropogon prinoides, X50 (Douval-Jouvé). Fig. 11, Cyperus
rotundus, var. Hydra, X55. Fig. 12, Kyllingia pumila, X55. Fig. 13, Fimbristylis autumnalis, X55. Fig. 14, Rhynchospora capillacea, X55. Fig. 15,
Carex vulpinoidea, X46. Fig. 16, C. Pennsylvanica, X55. Fig. 17, C. Careyana, X55. Fig. 18, C. laxiflora, var. latifolia, X55.