Ketchup — Structure of the Tomato

HISTOLOGY OF THE TOMATO AND OF THE RESULTING KETCHUP.

STRUCTURE OF THE TOMATO.

=Pericarp.

= The tomato is a typical berry, the ovary wall, free from the calyx, forming the fleshy pericarp, which encloses chambers filled with a clear matrix, containing the seeds.

The pericarp consists of an outer tough membrane, the epidermis, a more or less thick layer of parenchyma tissue, the pulp, and an inner thin, delicate membrane, the lining layer of the loculi or chambers in which are the seeds.

The epidermis consists of a single layer of cells which have a very thick continuous cuticle about one-half of the diameter of the whole cell.

The cuticle differs in chemical composition from the rest of the cell walls, being impervious to water, and resisting rotting longer than do the cellulose walls.

As it is continuous over the whole of the fruit, the skin can be readily separated from the other tissues.

Hot water facilitates the removal of the skin, as it causes the cellulose of the walls to swell more than the cuticle, producing an effect as of shrinkage of the outer wall and a consequent curling of the skin.

The radial walls of the epidermis are short and irregularly thickened, leaving pits in the walls, and giving them a beaded appearance.

The skin constitutes about 1. 3 per cent of the tomato.

The layers of parenchyma just beneath the epidermis are closely united and flattened, with their adjoining walls irregularly thickened.

On account of their position, they are called hypoderm.

In the tomato the hypoderm consists of two or three layers of cells, parts of which usually separate with the epidermis.

Below these cells are the thin-walled parenchyma cells, which are approximately globular, vary considerably in size, are very loosely held together, and have many intercellular spaces.

These cells constitute the mass of the pulp, and with the juice constitute 96. 2 per cent of the tomato.

The layer of cells which lines the chambers has the typical leaf epidermal structure, the wavy outlines, the hollows and protuberances of adjoining cells fitting one another so that they form a continuous layer.

They are also flattened laterally.

The structure can be understood readily when it is known that the pericarp is really a metamorphosed leaf and that the outer side of the leaf forms the inner wall of the ovary.

The chambers of the tomato are filled with a clear, slimy matrix in which the seeds are embedded.

The matrix consists of parenchyma cells of various sizes and with delicate walls, and a small nucleus.

The cells are massed loosely, and can be separated readily.

In those cells, as well as in the wall cells, are starch grains which vary in size, being round or approximately so, and having the hilum, when visible, a straight line to one side of the center.

=Coloring Matters.

= In the parenchyma cells are two coloring matters, one yellow, which is amorphous in structure, and the other red and of crystalline form.

The sap contains a yellow color in solution which differs in its reactions from those in the pulp.

=Red Color in Tomatoes.

= The red coloring matter in tomatoes is in the form of irregularly shaped crystal-like chromoplasts, which occur in masses of various sizes.

They are present in largest amounts usually in the protoplasm which lies close to the ectoplasm and in that surrounding the nucleus.

They vary from sharp, bright-colored forms to those more or less blunt in outline, and dull in color.

They may be situated largely in the periderm, the soft parenchyma beneath the periderm, or through the whole mass of the parenchyma with the exception of the matrix surrounding the seeds in the loculi.

In tomatoes having the color in the periderm a considerable amount is lost by adherence to the skin.

The chromoplasts are not affected by rotting to the same extent as are the other constituents of the cell; they can be found floating free in the debris from rotted cells, still retaining considerable color.

They lose their color gradually, in some varieties much more rapidly than in others.

In stored pulp which has fermented, the color may be faded to a dull yellowish brown.

In tomatoes intended for ketchup where a bright red color is desirable, care should be used in the selection of a variety having the chromoplasts bright, properly oriented, and in sufficient quantity.

=Vascular Bundles.

= In the pulp of the tomato are found strands of vascular tissue, entering from the stem, and dividing and ramifying through the soft pulp.

These consist of long tubes with thin walls, some of which have a strengthening band in spiral form on their interior walls, the associated cells being without any special marking.

The strands vary in size from those having a few tubes to those having a large number.

=Seeds.

= The seeds of the tomato are small, flattened, yellow bodies covered by a clear gelatinous membrane.

Their peculiar characteristic is the out-growth of hairs of varying lengths.

The seeds constitute about 2. 5 per cent of the weight of the tomato.