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In this article we will discuss about some instruments that are commonly used in a laboratory.
Instruments for Field Collection:
While you are on field collection trip, you should have the following instruments with you:
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1. One pocket lens
2. One good fixative (F.A.A.)
3. Collection bottles (three dozen)
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4. Full-sized blotting papers (three dozen)
5. Newspapers pieces (two dozen)
6. Polythene bags (four dozen)
7. Rubber bands (four dozen)
8. Plant press-made up of two flat plywood sheets and a thick, strong cord
9. Glass-marking pencil
10. Departmental labels.
Dissecting Microscope:
It is actually a simple microscope that consists of only one lens unit. This lens unit may even be an ordinary magnifying glass. Dissecting microscope is used either for dissecting the material or for less magnifications, i.e., only 6X, 12X or rarely 20X. It is mainly used for embryo separation, taxonomic studies, etc.
A dissecting microscope (Fig. 3) consists of a basal foot and a limb. The ‘stage’, made up of a simple glass plate, is attached to the limb. For the light adjustment purposes, a mirror is attached to the limb under the stage. Mirror can be moved vertically with the help of an adjustment screw.
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At the tip of the limb is present a folded arm, on which a lens of definite magnification (6X, 12X, etc.) is fitted. Folded arm is moved to keep the lens in the desired position on the stage.
The material to be viewed or dissected is placed on the stage. The eye is placed close to the lens. Folded arm is tilted to bring the lens over the material. Light is adjusted by the movement of the mirror. Focussing is done with the help of adjustment screw.
Compound Microscope:
1. The instrument is so named because it consists of two or more lens systems (Figs. 1, 4).
2. At the top is present the ocular lens. It can be turned around or may be removed. At the top of ocular lens is written 5X or 10X signifying the 5 times or 10 times magnification, respectively.
3. Just below the ocular is a body tube, the bottom end of which contains a circular piece called nose piece. It contains three lenses called objective lenses. Nose piece can be rotated to change the position of objectives.
4. The flat platform present below the objectives is called stage.
5. On the arm of the microscope are present two knobs called coarse adjustment knob and fine adjustment knob.
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6. Out of the three objectives, the shortest is the low power objective. It has the largest lens but its magnifying power is least of the objective lenses. On the objective may also be written 10X similar to ocular lens. It means if a 10X ocular lens is used the magnification is 10 x 10 = 100 times.
7. The other objective is high power objective. Its magnification is equal to the number written on it multiplied by the power of ocular, i.e., 5X or 10X (objective x ocular).
8. The third objective is called oil immersion. Generally, it contains a black band around the lower end. Use a drop of oil on the slide at the time of studying with the oil immersion objective. Its magnification can be estimated as ocular x objective.
The use of oil (e.g., cedar-wood oil) is essential in order to keep the light rays properly aligned with the small objective.
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9. Just below the stage is the condenser. Its function is to gather light from the mirror and to direct it to the objective lens. Condenser may be lowered or raised by a knob present on one side of the microscope beneath the stage.
10. Condenser contains a shutter called Iris diaphragm.
11. Just below the condenser is present a mirror having its one surface flat and other concave? Use the concave surface in the day light. Flat surface of the mirror is used when electric lamp is used.
Precautions:
1. Clean the ocular and objective lenses with lens paper, and do not remove them.
2. While studying an object, learn to keep one hand on the fine focus knob and focus continuously up and down.
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3. While studying any kind of preparation, do not tilt the microscope.
4. Leave the low power objective in place after finishing all the observations.
5. To examine an object, always first use the low power and then the other objectives.
6. Never allow an objective lens to strike either the stage or a slide while focussing.
7. Use always the fine adjustment with high power objective.
8. All wet-mount preparations should be pre-covered by a cover slip.
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9. Avoid the habit to remove the parts of the microscope.
10. Do not use oil immersion objective without oil.
11. Diaphragm should be wide open while using oil immersion objective.
Preparation of Some Fixatives, Stains and Reagents:
1. Formalin-Aceto-Alcohol (F.A.A.):
50% or 70% ethyl alcohol 90 c.c.
Glacial acetic acid 5 c.c.
Formalin 5 c.c.
It is the most commonly used preservative and commonly called as ‘standard-preservative’.
2. Safranin:
Safranin 1 gm
Water (or 50% alcohol or 70% alcohol) 100 c.c.
3. Fast green:
Fast green 1 gm
90% alcohol 100 c.c.
4. Cotton blue:
Cotton blue 1 gm
Lactophenol 100 c.c.
5. Acid alcohol:
HCl 10 to 20 drops
Alcohol 100 c.c.
6. Acid water:
HCl 10 to 20 drops
Water 100 c.c.
7. Lactophenol:
Phenol 100 gm
Lactic acid, glycerine and water 100 c.c. each
8. Glycerine:
Glycerine 10 to 15 c.c.
Water 100 c.c.
Formalin one drop.
Study of Plant Material:
Take the fresh or preserved material and first study its external morphology with unaided eye or with the help of a magnifying lens or dissecting microscope. If the material is microscopic, stain it with a suitable stain and mount in glycerine and then study under the low and high powers of a compound microscope.
For observing the anatomical details, cut the sections of your material in various planes like transverse section (T.S.), longitudinal sections (L.S.) like radial longitudinal section (R.L.S.) or tangential longitudinal section (T.L.S.) as under:
Transverse Section (T.S.):
It is cut by passing the edge of the razor at right angles to the longitudinal axis of the cylindrical organs such as roots, stems, etc.
However, in case of the dorsiventral organs (e.g., leaf, thallus of bryophytes, etc.), the transverse section is being cut in vertical plane and hence it is called vertical transverse section or V.T.S
Longitudinal Section (L.S.):
It is cut by passing the edge of the razor at right angles to the transverse axis of the cylindrical organs, such as roots, stems, etc.
If the longitudinal section is cut along one of the radii, it is called radial longitudinal section or R.L.S.
But if the L.S. is cut along the tangent, it is called tangential longitudinal section or T.L.S. (Fig. 5).
Method of Section Cutting:
A good quality razor should be used for section cutting. Before section cutting the razor should be sharpened on a hone (fine grit-stone). Sharpening is done by sliding the razor obliquely and uniformly over the wet hone. This process is called honing.
After the honing process, the razor is further sharpened by moving for some time over a leather strap. This process is called stropping. The leather strap should be first oiled before being used.
Pith (i.e., pieces of carrot, potato, radish, etc.) is used for cutting sections of soft and delicate materials. At the time of using the pith, cut it longitudinally up-to half of the length, and then remove the spitted piece by cutting one strip transversely. Insert the material in the centre and replace the piece of pith over it as shown in Fig. 5.
For cutting the section, hold the pith (along with the material) in your left hand between the thumb and the fingers. Keep the forefinger in somewhat horizontal position and thumb at a little lower height. Hold the razor in your right hand in such a way in a horizontal position that its blade and handle form a right angle.
Move the razor quickly over the pith (containing material) and complete the stroke in one action. Make 10 to 15 uniform strokes of the razor one after the other. You will get a few complete and thin sections. Immerse the sections in a watch glass containing water with the help of a fine brush. The material in pith and the razor blade should be kept flooded with water during the entire process.
Select thin and complete sections for staining. Thin sections usually keep on floating over the water surface. Only uniformly cut, thin and complete sections should be stained.
