Quality control methods for

Fig. 1. Alignment of the stage micrometer and the ocular micrometer 
Method 
Place the specimen on the microscope stage and focus on the object to be 
measured. Superimpose the ocular micrometer scale and read off the dimensions 
of the object. Multiply the number of scale divisions by the micrometer value to 
give the actual dimension in micrometres. By this method, using a 40x objective 
and a 6x eyepiece, measurements are correct to the nearest 2 µm, i.e. a dimension 
of 20 µm is liable to an error of 2 µm, or 10%, or ±5%; a dimension of 100 µm is 
liable to an error of 2% or ±1%. 
For curved and elongated objects, the measurement of lengths may be made 
using a microscope equipped with a drawing apparatus or a camera lucida. The 
instrument should be set up so that the image of the object, the drawing paper 
and the pencil are in focus simultaneously. With the stage micrometer in place, 
trace the lines of the stage micrometer scale upon the paper fastened on a 
drawing board. Tilt the drawing board, if necessary, until the divisions drawn 
upon the paper are equally spaced. The magnification is determined by 
measuring the distance between selected lines on the drawing paper and 
dividing by the distance between the corresponding lines on the stage 
micrometer. Place the specimen on the microscope stage and trace the image of 
the object on the paper. Superimpose a coloured thread along the length of the 
object drawn on the paper and after straightening it, measure the length of the 
thread by means of a ruler graduated in millimetres; divide the measured length 
by the magnification to give the actual length of the object. 
Leaf stomata 
 
Types of stoma 
In the mature leaf, four significantly different types of stoma are distinguished 
by their form and the arrangement of the surrounding cells, especially the 
subsidiary cells (Fig. 2): 

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Quality control methods for medicinal plant materials 
• The anomocytic or ranunculaceous (irregular-celled) type; the stoma is 
surrounded by a varying number of cells, generally not different from 
those of the epidermis. 
• The anisocytic or cruciferous (unequal-celled) type; the stoma is usually 
surrounded by three or four subsidiary cells, one of which is markedly 
smaller than the others. 
• The diacytic or caryophyllaceous (cross-celled) type; the stoma is 
accompanied by two subsidiary cells, the common wall of which is at 
right angles to the stoma.
• The paracytic or rubiaceous (parallel-celled) type; the stoma has two 
subsidiary cells, of which the long axes are parallel to the axis of the 
stoma. 
In describing an epidermis where certain stomata differ from the predominant 
type, the term applying to the majority of stomata is used. 
Determination of the stomatal index 
Place fragments of leaves, about 5 x 5 mm in size, in a test-tube containing about 
5 ml of chloral hydrate TS and heat on a water-bath for about 15 minutes or until