Texas Journal of Microscopy - Texas Society for Microscopy

Figure 47. Crystal sclereids of Nymphaea mexicana. Note
CaOx crystals imbedded in the cell wall of four different sclereids
in the storage root. Adapted from Van De Veire, 1997.
On a visit to the JOEL office in Peabody, Massachusetts, I discovered
some interesting leaf-like “plants” growing on the large
granite boulders which were frequent in the area (Fig. 45). At
the time, I was taking a course on the EMS 200 TEM that we
had just purchased. I took a few of these leaf-like structures back
home and determined that they were Umbilicaria pennsylvanica,
a lichen species. I also found that one of its common names
was “Washington’s Rock Tripe.” This lichen is associated with
George Washington because when the Revolutionary War soldiers
he commanded at Valley Forge were hard pressed for food,
they boiled and ate the rock tripe.
I was fascinated by rock tripe, not only because they had many
crystals of CaOx, but because of their “reputation” as “emergency
food.” Large multi-interpenetrant twins and single crystals
were found on the surface and in the interior of these interesting
“plants.” On a later trip, I collected a large number of the leaf-like
thalli for SEM studies (Fig. 46). I studied both the dried thalli and
hydrated fixed specimens. I also boiled them for some time and
found that the plentiful crystals of CaOx did not dissolve. Calcium
oxalate is insoluble in water (Merck Index), even in boiling water.
Soldiers of the Revolution and/or others that have eaten U. pennsylvanica
would have got a good dose of oxalate when the crystals
dissolve in their stomach acids. On another occasion, while
in Massachusetts, I had the opportunity to work with (then) the
newly developed ESEM, and among other things, I collected U.
pennsylvanica to look at the thalli in a hydrated state. The walls
were much thicker and wrinkles in the cell contours were erased
when hydrated. In some cases, it appears that the CaOx crystals
form in the fungal component of the lichen since examples of
crystals attached to the hyphae were found. The crystals appear
to be embedded on the surface of the thallus and thereby partly
surrounded by hyphae. However, some crystals seem to be free
within the “tissues” of this “plant.” Although twinning is com-
mon, many single large
prismatic crystals of
CaOx dihydrate were also
present (Fig. 46).
One of the last students
to work on plant crystals
in my laboratory was
Jackie Van De Veire. The
subject of Jackie’s thesis,
completed in 997,
was on the large multi
branched crystalliferous
sclereids which occur in
the storage roots of Nymphaea
mexicana (Van De
Veire, 997). This water
lily produces unique
storage roots in which
large masses of starch
are stored in the cortical
parenchyma. In addition,
Figure 48. Sandra Westmoreland,
“The egg shell lady”, about 1998.
Photo by HJA.
these roots produce very large sclereids which have crystals embedded
in their cell walls (Fig. 47). The sclereids are unique as
they may have five or more cellular branches, all of which run in
a parallel direction and more or less in one plane. The arms of
these sclereids extend by intrusive growth forcing their way between
other cells in the cortex. The sclereids are also notable for
the large CaOx dihydrate crystals that are embedded in the cell
wall. Jackie worked out the morphology and development of these
unique cells and she established the role these storage roots play
in the life history of N. mexicana.
Crystals are not just found in association with specialized cell
types. They are often found in the cytoplasm or in organelles such
as microbodies, mitochondria and chloroplasts and even in the
cytoplasm proper. I studied them in corn phloem (Plate 37) and
in Malpigia glabra flowers, which have cells with crystals in their
mitochondria. These crystals may occupy much of the volume of
some mitochondria. The lattice planes of these crystals can be
seen with the TEM (Plate 37: -6). The line to line measurements
can be on the order of 50- 00 Å. Proteins are probably the only
molecules which are large enough to form lattice planes of these
dimensions. I always have assumed that the above crystals were
proteins which underwent crystallization being present in excess
in the mitochondrion. These “protein” crystals often seem to be
nucleated on mitochondrial membranes. Malpigia also produces
large “protein crystals” in the cytoplasm (Plate 37: 4).
Crystals are also found in single cell organisms. The bacterial
magnetosomes are partly crystalline iron sulfide crystals and are
found in a few bacterial species. Euglena granulata is a eukaryotic
single cell organism that produces crystals. The cells of Euglena
are somewhat complex; they have a nucleus, mitochondria, chloroplasts,
an intricate folded external structure called the pellicle
which allows them to change shape, a very large Golgi apparatus
with 30 to 50 or more cisternae, a contractile vacuole, and two
flagella, one which is associated with the large eyespot. The cells
have the ability to change their shape from spherical to elongated
and back, and to swim backward or forward. These characteristics
certainly establish Euglena as one of the “one-cell wonders”.
E. granulata also makes crystals, hence the specific name
granulata. The crystals can be seen as bright spots when viewing
cells under polarized light (each spot representing a single crystal).
The E. granulata crystals are believed to be calcium oxalate
as they are extracted in the same manner as the CaOx crystals
in higher plants; however, unambiguous identification of these
crystals has not been achieved yet. The specimens I studied came
Tex. J. Micros. 38: , 2007
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