The various simple tissues in plants are parenchyma, collenchyma and sclerenchyma.
Parenchyma forms the major component within organisms, which are generally isodiametric and spherical, oval, round, polygonal or elongated in shape.
The walls of parenchyma are made up of cellulose either closely packed or have small intercellular spaces and performs photosynthesis, storage, secretion.
Fig. Parenchyma tissue
The collenchyma occurs in layers below the epidermis in dicotyledonous plants without intercellular spaces , found either as a homogeneous layer or in patches and consists of cells which are much thickened at the corners due to a deposition of cellulose, hemicellulose and pectin.
Collenchymatous cells may be oval, spherical or polygonal and assimilate food when contain chloroplasts.
They provide mechanical support to young stem and petiole of a leaf.
Fig. Collenchyma tissue
Consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits.
They are usually dead and without protoplasts.
The fibres are thick-walled, elongated and pointed cells.
The sclereids are spherical, oval or cylindrical, highly thickened dead cells with very narrow cavities known as lumen.
These are commonly found in the fruit walls of nuts; pulp of fruits like guava.