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In my last article in Micscape (April 1996) I showed photomicrographs of desmids, comparing those taken using ordinary transmitted light with others to which Indian ink was added to the water to show up the mucilage.
This article shows the effect of using polarised light. A polarising microscope; (Petrological microscope) is not essential. A small piece of polarising sheet, one lens of a pair of polaroid sun glasses will do, is placed in the light path beneath the stage, another piece is put above the specimen, a piece cut from the other sun glass lens will do. If you have a binocular microscope it can be put beneath the binocular head, if using a monocular a piece can be put in or above the eyepiece, either the upper or lower piece must be turned to the extinction point- X-polars.
Desmids will sometimes exhibit intense activity within the cell, the whole protoplasm becoming a mass of swarming vibrating granules, when in this state I have found the cell contents will show up when viewed with X- polars. First view with normal transmitted light then when the polarisers are put into place other desmids in the field of view not showing the vibrating granules will disappear, only the vibrant desmids react to the polarised light.
Fig 1. shows the desmid Pleurotaenium ehrenbergii in ordinary light.
Fig 2. shows the same desmid in polarised light. Note, the crystals of barium sulphate, (Brook et al. 1988) can just be seen in the apical vacuole.
Fig 3. shows the desmid Closterium intermedium, the chloroplast has been attacked by a fungus, the fungal body is showing intense activity.
Fig 4. is of the same cell in polarised light, only the fungal body and the cell wall can be seen, the rest of the chloroplast with no moving granules can not be seen, other algae in the 'photo' has also disappeared.
Brook A.J. Grime G.W. & Watt F. (1988) A STUDY OF BARIUM ACCUMULATION IN DESMIDS USING THE OXFORD SCANNING MICROPROBE (SPM). 0168-583X/88 Elsevier Science Publishers BV.
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