The three simple tissues

Simple permanent tissues are told apart by the shape of the cells and the nature of the cell wall. On those two grounds there are three of them.

Figure to be added

Figure 1.6 — the three simple permanent tissues drawn side by side: parenchyma as rounded cells with thin even walls, collenchyma as cells whose walls are thickened only at the corners where three cells meet, and sclerenchyma as cells with walls thickened evenly all round, leaving a small empty space in the middle.

Tissue	Living?	The cell wall	Main job
Parenchyma	Living	Very thin, cellulose, even all round	Storage, photosynthesis, and support by turgidity
Collenchyma	Living	Cellulose, thickened at the corners only, so unevenly thick	Support and mechanical strength, while the plant is still soft
Sclerenchyma	Dead	Lignin laid on cellulose, thickened evenly all round	Support and mechanical strength, permanently

The three simple permanent tissues at a glance. Each gets a skill of its own from here.

Reading the table

The three rows are a sequence, not a list. Going down it the wall gets thicker and the cell gets less alive, and the job shifts from doing things to holding things up. A plant needs all three at once, which is why a stem section shows all three at once.

Wall thickening is the whole story

Thin wall, corner-thickened wall, uniformly lignified wall. That single feature separates the three tissues, decides whether the cell can stay alive, and settles what the tissue is for. If you remember one column of this table, remember the third.