Exine (outer wall)The tough outer wall of the grain. Its surface is often sculptured with ridges, warts or spines.
Intine (inner wall)The inner wall of the grain. The pollen tube grows out from it.
Tube cellThe cell that grows a pollen tube. It is also called the vegetative cell.
Tube nucleusThe tube cell's nucleus. It moves into the pollen tube.
Generative cellThe cell that divides to make two sperm cells.
ApertureA thin spot or gap in the outer wall. The pollen tube comes out here.
On a stigma 5
Pollen grainA grain that lands on a stigma grows a tube.
StigmaThe tip of the pistil, where pollen lands. Its surface holds the grains fast.
Pollen tubeA tube that grows from the grain toward an ovule. It carries the sperm cells.
Sperm cellsTwo male cells carried down the tube. One joins the egg cell.
StyleThe stalk between the stigma and the ovary. The pollen tube grows down through it.
How this list was compiled: Every name checked on 2026-10-03 and kept only where two of these use it. (1) J. M. Coulter and C. J. Chamberlain, Morphology of Angiosperms, 1903, chapters VI and VII (public domain), https://archive.org/details/morphologyofangi00coulrich : each young microspore is invested by a wall that becomes two layers, the inner one (intine), which later develops the pollen-tube, and the outer layer (exine), which is cutinized and variously sculptured with ridges, warts or spines; there are thin spots in the exine for the exit of pollen-tubes, one in most monocotyledons and two to many in most dicotyledons; the microspore divides to form the tube nucleus and the generative cell; the tube-cell of the pollen-grain pushes a protrusion of the intine through the exine that develops into the pollen-tube, which passes among the cells of the stigma and enters the style. (2) Wikipedia, Pollen and Pollen tube, https://en.wikipedia.org/wiki/Pollen and https://en.wikipedia.org/wiki/Pollen_tube : a tough outer wall, the exine, and an inner wall, the intine; the exine is the part preserved in the fossil record; pollen apertures are regions of the wall with a thinner exine; each grain holds a vegetative (tube) cell and a generative cell; the tube cell makes the pollen tube; the generative cell divides into two sperm cells; the nucleus of the tube cell passes into the tube; the tube grows down the style to an ovule and one sperm cell fertilizes the egg cell. (3) C. S. Gager, Fundamentals of Botany, 1916, sections 389 to 391 and figure 324 (public domain), https://archive.org/details/fundamentalsofbo00gagerich : the stigma is the surface that receives the pollen-grains and holds them fast with a sticky substance, in some plants with tiny hairs; the style; the young pollen grain with generative nucleus and tube nucleus; the generative cell divides to form the sperm-cells, in some plants before pollination and in others after the pollen-tube has begun to form. (4) A. A. Dobritsa and S. H. Reeder, Formation of pollen apertures in Arabidopsis requires an interplay between male meiosis, development of INP1-decorated plasma membrane domains, and the callose wall, Plant Signaling & Behavior, 2017 (Ohio State University; abstract read), https://pmc.ncbi.nlm.nih.gov/articles/PMC5792127/ : apertures are formed by gaps in the pollen wall exine, in a pattern that differs from species to species. Licence: own work
The drawing: Drawn for this site on 2026-10-03 from plain geometry; own work, nothing traced. Licence: own work
How it works
This pollen cell diagram shows that a pollen grain is more than one cell. Inside two walls sit a tube cell and a generative cell. The second drawing follows a grain that lands on a stigma.
Read the full guide
Two walls, two cells
The outer wall is the exine and the inner wall is the intine. Inside them the tube cell holds the tube nucleus and the generative cell.
From stigma to ovule
A grain on a stigma pushes a pollen tube out through an aperture. The tube grows down the style toward an ovule. It carries two sperm cells, made when the generative cell divides.
In some plants the generative cell divides before the pollen is shed, so the grain holds three cells.
The number of apertures differs from plant to plant. This grain is drawn with one.
Questions and answers
Is a pollen grain a single cell?
No. A ripe pollen grain of a flowering plant holds two or three cells inside its walls: a tube cell, and a generative cell or the two sperm cells it divides into.
What are the exine and the intine?
The two walls of a pollen grain. The exine is the tough outer wall, often sculptured with ridges, warts or spines. The intine is the inner wall, and the pollen tube grows out from it.
What does the generative cell do?
It divides once to make two sperm cells. The pollen tube carries them down the style to an ovule, where one joins the egg cell.
What is a pollen tube?
A tube that the tube cell grows after the grain lands on a stigma. It passes down through the style to an ovule and delivers the two sperm cells.