Quantitative microscopy or determination of some pharmacognostic parameters are useful for setting standards for crude drugs. Quantitative microscopy is used for evaluation of crude drugs. It includes vein-islet number, vein-termination number, stomatal number, stomatal index and palisade ratio.
Stomata: A stoma is made up of a pair of identical guard cells, forming a pore in centre through which gaseous exchange takes place.
Types of stomata
|Types of stomata||Example of drug|
|1.Paracytic or Rubiaceous or parallel- celled stomata||Cocca leaf, senna leaf|
|2.Diacytic or caryophyllaceous or cross-celled stomata||Peppermint, Vasaka|
|3. Anisocytic or cruciferous or Unequial celled stomata||Belladona, Datura|
|4. Anomocytic or ranunculaceous or irregular celled stomata||Digitalis, Lobelia|
Trichomes: An elongated tubular outgrowth of an epidermal cell is termed as trichome.
Function — Protective, secretion of essential oil, absorption of water.
Types of Trichomes
|Types of trichomes||Example of drug|
|1) Covering or non glandular trichomes
|| Nux- vomica, StrophanthusCannabisLobelia
|2) Covering trichomes (Multi cellular) a) T. shaped trichomes||Artemisia, Pyrethrum|
|3) Covering unbranched trichomes
|4) Glandular trichomes
||VasakaDigitalis pupurea,Digitalis thapsi, Cannabis sativa|
Types of calcium oxalate crystals
|Raphides||Squill, Rauwolfia, Cinnamon|
|Acicular crystals||Squill, Ipecacauanha|
- Palisade ratio: Average no. of palisade cell beneath each epidermal cell. It can be determined with powdered drugs.
- Vein- islet number: No. of vein-islets per sq. mm of the leaf surface midway between midrib and margin.
- Vein – termination number: No. of vein- islets termination per sq. mm of the leaf surface midway between midrib and margin.
- Stomatal number: Average no. of stomata per sq. mm of epidermis of the leaf.
- Stomatal index: Percentage which the number of stomata forms to the total number of epidermal cells each stoma being counted as one cell.
Lycopodium Spore method:
Lycopodium spore method is a method for the study of powdered drugs having well defined particles like pollens, starch grains, single layered tissues or some other types of uniformly thick particles. It is used when chemical and other methods of evaluation of crude drugs fail as accurate measures of quality. On average 94000 spores per mg of powdered lycopodium are present.
N×W×94,000× 100 = % purity of drug