The biological part of a herbarium specimen typically consists of a dried portion of a plant, typically a piece of a stem with attached leaves, flowers and/or fruit. The sample has been pressed and thouroughly dried and will last for hundreds of years if kept dry and secure from insect attack and physical damage.
It is usually quite difficult to identify plants from leaves and stems alone and botanists try to collect specimens with flowers or fruit, and preferrably both.
Sometimes microscopic characters are needed for identification and leaves, flowers and fruit may be removed from the specimen for examination under a microscope. After examination, the remaining fragments are placed in packets which are secured to the herbarium sheet.