Histology of medicinal plants

by William James Mansfield

The cells forming mechanical tissues are: bast fibres, wood fibres, collenchyma cells, stone cells, testa epidermal cells, and hypodermal and endodermal cells of certain plants. The walls of the cells forming mechanical tissues are thick and lignified, with the exception of the collenchyma cells and a few of the fibres. Lignified cells are as resistive to pulling and other stresses as similar sized fragments of steel. The hardness of their wall and their resistance to crushing explain the fact that they usually retain their form in powdered drugs and foods.

BAST FIBRES

One of the most important characters to be kept in mind in studying bast fibres is the structure of the wall. In fact, the author’s classification of bast fibres is based largely on wall structure. Such a classification is logical and accurate, because it is based upon permanent characters. Another character used in classifying bast fibres is the nature of the cell, whether branched or non-branched. In fact, this latter character is used to separate all bast fibres into two fundamental groups—namely, branched bast fibres and non-branched bast fibres. The third important character utilized in classifying fibres is the presence or absence of crystals.

Bast fibres are classified as follows:
1. Crystal bearing.
2. Non-crystal bearing.

The crystal-bearing fibres are divided into two classes:
1. Of leaves.
2. Of barks.

The non-crystal bearing are divided into:
1. Branched.
2. Non-branched.

The branched and non-branched are divided into four classes:
1. Non-porous and non-striated.
2. Porous and non-striated.
3. Striated and non-porous.
4. Porous and striated.

CRYSTAL-BEARING BAST FIBRES

The crystal-bearing fibres are composed (1) of groups of fibres, (2) of crystal cells, and (3) of crystals. In these cases the groups of fibres are large, and they are frequently completely covered by crystal cells, which may or may not contain a crystal. The crystals found on the fibres from the different plants vary considerably in size and form. As a rule, the fibres when separated are free of crystal cells and crystals. This is so because the crystal cells are exterior to the fibres, and in separating the fibres during the milling process the crystal cells are broken down and removed from the fibres. It is common, therefore, to find isolated fibres and crystals associated with the crystal-bearing fibres. The fibres which are crystal-bearing may be striated or porous, etc.; but owing to the fact that the grouping of the fibres and crystals is so characteristic, little or no attention is paid to the structure of the individual fibres.