THE AMERICAN
MONTHLY
MICROSCOPICAL JOURNAL.
VOL. XIII.
JUNE, 1892.


On the Continuity of Protoplasm through the Cell Walls of
Plants.
BY W. J. BEAL AND J. W. TOUMEY,
AGRICULTURAL COLLEGE, MICH.
Sachs, in 1863, proved the continuity of protoplasm from cell
to cell through sieve plates, and in 1880 made the remarkable
statement that this continuity was universal in plants. He said,
"Every plant, however highly organized, is fundamentally a protoplasmic body forming a connected whole, which, as it grows
on, is eternally clothed by a cell membrane, and internally traversed by innumerable transverse and longitudinal walls."*
Considering the difficulty of successfully demonstrating the continuity of protoplasm in many parts of plants, more especially

*Walter Gardiner, in Philosophical Transactions of the Royal Society of London, Vol. 174, P. 817.


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where the cell walls are thin, and with a view to finding which
plants of those accessible to most students in our country are
most suitable for the purpose, we began the work by examining
the cortical layer of one or more species of about seventy-five
genera of native and cultivated exotic trees and shrubs. With-
out going into details in regard to all the various methods which
have been tried by Sachs, Gardiner, and others, we will merely
state that at first beginning, a thin fresh tangential section was
made with a razor and at once a drop of strong sulphuric acid
from a glass rod was placed upon it. After one to three minutes, depending on the thickness of the cell walls of the specimen
examined, the sections were rapidly washed in water, and
stained with iodine or analine blue.

Chloriodide of zinc was also tried. But the most satisfactory results were obtained by placing a thin section in a solution of
iodine, until it turned brown. Then wash, and then run strong
sulphuric acid under the cover-glass, and soon, again, draw out
the acid, replacing it by water. After washing well, mount in
glycerine and color with green or blue analine.

In these experiments, a great deal of time and labor for weeks
may here be passed over by a mere mention of the fact, calling
it dead work." Now for the results: The large masses of protoplasm in all the cells properly treated were very pronounced,
and from each mass extended arms or strands in every direction.
Each arm in a cell exactly approached and met or seemed to
almost meet one from an adjoining cell. In some places, in every
species examined, a continuous strand seemed to extend from
one cell to the next one, but this was very likely due to some imperfect work in making the experiment. In most instances there
was a light line, through which the connection could not be
successfully traced. At this place the tips of the strands were
swollen and between them a light, hazy look was very common.

The question to be demonstrated was the presence of delicate
threads of protoplasm passing from the swollen tip of one strand
to the swollen tip of a contiguous strand in the next cell. In the
cells of the endosperm of palms the walls are very thick, and the
space between the tips of contiguous strands rather prominent;
but in the cortical layer of our woody plants the cell wall is rather
thin, and the space between the tips of the strands is a very narrow one. To trace threads across this narrow passage is difficult
and often unsatisfactory, as the threads are very short. We employed a Spencer's one-eighteenth-inch immersion objective.

Among the most satisfactory of the many specimens of cortex
examined was that of the common lilac, where the sections were
taken from large-sized twigs two to three years old. Viburnum
opulus (snow ball) was much the same. In specimens of our
hawthorns the strands were slender and longer, but the threads
joining their tips showed very well. Perhaps the best one of all
was taken from the cortex of Alnus glutinosa. Here the
 
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strands are of good size. At the middle lamella the connecting
threads of protoplasm are three to seven or more in number, and
bulge outward, the whole somewhat resembling a barrel in shape.
Unfortunately a drawing of the alder was mislaid. The drawing
of the endosperm of Heterospathe elata, a palm seed (Fig. 3),
has been copied from the work of Mr. Gardiner, and very closely
resembles that of the alder, above referred to. In A is seen endosperm of Heterospa the elata, showing threads of the tips of
four contiguous strands. The middle lamella is but little developed; in B, ripe endosperm of Phoenix dactylifera after treatment-one cell, with parts of several others. The strands of protoplasm extending out from the central mass in the cells of Amelanchier (Fig. 1) are often forked near the tips.

Fig. 1.
X410
Fig. 2.
x750
Fig. 3.

The specimen is one of the best examined. The cells are not
large, but are comparatively long, and having exceedingly long
protoplasmic strands. From one cell (A) many pointed strands
of protoplasm seemed to radiate in all directions, their form of
cells were numerous, and in some cases strands extended to other
cells. The peculiar point illustrated by B, C, D, and E is the
forked appearance of protoplasmic strands at the point of junction
between the cells. Here in many cases the connection seems to
be broken, but in above, as in E, exceedingly fine threads apparently unite the two strands. The middle lamella is easily seen
in this specimen, and it is here where we always find the break, if
any, in the connecting strands.

In Cratagus (Fig. 2) the continuity is very pronounced. The
middle lamellæ are distinct. At the middle lamella there is a
difference apparently in the strands of protoplasm. Strands do
not appear as dense at this point as elsewhere. Strands in all

132
cases come to the middle lamella at the same point as those of
the neighboring cells.

In the thick-walled cells of the ripe endosperm of many palms,
Mr. Gardiner demonstrated that extremely delicate threads not
only passed from tip to tip of the strands of protoplasm, but
through the thick walls as well.

We give the names of those examined:
SECONDARY CORTEX.
Acer platanoides, L.
Aesculus glabra, Willd.
Ailanthus glandulosus, Desf.
Alnus glutinosa, Gaert.
Amelanchier Canadensis, T. & G.
Amorpha fruticosa, L.
Berberis vulgaris, L
Betula alba, L.
Betula lutea, Michx, f.
Calycanthus Floridus, L.
Caragana arborescens, Lam.
Carpinus Americana, Walt.
Carya alba, Nutt.
Castanea pumila, Mill.
Catalpa speciosa, Warder.
Celastrus scandens, L.
Celtis occidentalis, L.
Cladrastis tinctoria, Raf.
Cornus stolonifera, Michx.
Corylus Americana, Walt.
Crataegus tomentosa, L.
Cytisus laburnum, L.
Dirca palustris, L.
Elæagnus hortensis, Marsch.
Euonymus atropurpureus, Jacq.
Fraxinus sambucifolia, Lam.
Gaylussacia resinosa, T. & G.
Gordonia, sp.
Gymnocladus Canadensis, Lam.
Hamamelis Virginiana, L.
Hydrangea paniculata, Siebold.
Ilex verticillata, Gray.
Juglans nigra, L.
Lonicera sempervirens, Ait.
Maclura aurantiaca, Nutt.

Magnolia acuminata, L.
Menispermum Canadense, L.
Negundo aceroides, Moench.
Philadelphus coronarius, L.
Picea nigra, Link.
Pinus strobus, L.
Populus alba, L.
Prunus Americana, Marshall.
Prunus Virginiana, L.
Ptelea trifoliata, L.
Pyrus malus, L.
Quercus alba, L.
Rhus capallina, L.
Ribes aureum, Pursh.
Ribes rubrum, L. var. subglandulosum, Maxmi.
Robinia pseudacacia, L.
Rosa setigera, Michx.
Salix cordata, Muhl.
Sambucus Canadensis, L
Sassafras officinale, Nees.
Smilax hispida, Muhl.
Spiræa trilobata, L.
Staphylea trifolia, L.
Syringa vulgaris, L.
Thuya occidentalis, L.
Tilia Americana, L.
Ulmus Americana, L.
Viburnum opulus, L.
Vitis riparia, Michx.
Xanthorrhiza apiifolia, L' Her.
Xanthoxyllum Americanun, Mill.

ENDOSPERM.
Iris versicolor. L.
Phoenix dactylifera, L.