Equisetum arvense with polarization
This is a transverse section through the stem of a Horse Hair (Equisetum arvense) in the internode region. It looks like it was created by a spirograph. Imaging under crossed polarizers shows the presence of optically active material. In general, In have noted high birefringence in the epidermal layers, however, in this case, the effect is quite marked in the middle layer. This is reported to be from deposition of silica in the epidermal cell walls. Although difficult to see here, vascular structures also show birefringent behavior, likely from ordered cellulose in the xylem. Specimen collected along the Dowagiac River, 25 May 2015. The 3X objective is not seller for getting even illumination, but it does make the point.
The protocol was as follows. Specimens fixed in FAA (formaldehyde, acetic acid, ethanol) 48 hr. Dehydrated in IPA at 35, 50, 70, 85, 91, 95, 99 %. Infiltrated with paraplast saturated xylene 48 hr followed by 3 Paraplast baths prior to embedding in Paraplast. Sectioned 7 um thick on a Spencer 820 microtome. Cleared in xylene, 5 min, 2X. Rehydrated in 99, 95, 80, 70 %IPA. Stained in Johansen's Safranin-O, Fast Green (24 hours in Safranin-O, 15 sec. in fast green). Cleared 2 X in xylene 10 min each and mounted with DPEX.
Photographed under crossed polarizers on a Spencer 42 petrographic microscope at original magnification of 30X using a Sony NEX-5N and a Leica MIKAS 1/3X adapter.
Equisetum arvense with polarization
This is a transverse section through the stem of a Horse Hair (Equisetum arvense) in the internode region. It looks like it was created by a spirograph. Imaging under crossed polarizers shows the presence of optically active material. In general, In have noted high birefringence in the epidermal layers, however, in this case, the effect is quite marked in the middle layer. This is reported to be from deposition of silica in the epidermal cell walls. Although difficult to see here, vascular structures also show birefringent behavior, likely from ordered cellulose in the xylem. Specimen collected along the Dowagiac River, 25 May 2015. The 3X objective is not seller for getting even illumination, but it does make the point.
The protocol was as follows. Specimens fixed in FAA (formaldehyde, acetic acid, ethanol) 48 hr. Dehydrated in IPA at 35, 50, 70, 85, 91, 95, 99 %. Infiltrated with paraplast saturated xylene 48 hr followed by 3 Paraplast baths prior to embedding in Paraplast. Sectioned 7 um thick on a Spencer 820 microtome. Cleared in xylene, 5 min, 2X. Rehydrated in 99, 95, 80, 70 %IPA. Stained in Johansen's Safranin-O, Fast Green (24 hours in Safranin-O, 15 sec. in fast green). Cleared 2 X in xylene 10 min each and mounted with DPEX.
Photographed under crossed polarizers on a Spencer 42 petrographic microscope at original magnification of 30X using a Sony NEX-5N and a Leica MIKAS 1/3X adapter.