Tropisms in Plants

Shown is a colour photograph of a cross-section of grass with roots growing down into soil.

A strip of green grass stretches across the photograph near the top. Below that, over half of the photograph shows its roots and the soil underneath. The roots are thin and white, tangled together like hair. All the roots are growing downward, deeper into the soil.

Shown is a colour illustration of two potted plants, one upright and one on its side. 

Both plants are in small brown pots, cut away to reveal the roots inside. The plant on the left is upright. Its stem grows upwards and its roots grow downwards. The plant pot on the right lies on its side. Its stem has curved to point upwards, perpendicular from its base. Its roots have curved downwards, towards the side of the pot on the ground.

Shown is a colour photograph of a cross section of bean seeds at different stages of germination, growing in soil.

Just over half the photograph shows underneath the soil's surface. A row of 6 bean seeds are shown, each at a different stage of germination. On the left is a seed with no growth, on the right is a pale green seedling with several leaves. In each one, the stem grows upwards from the seed, towards and through the surface. The roots grow downwards, deeper into the soil.

Shown is a colour illustration of two plants with a cross-section showing the roots underneath the soil. 

In the plant on the left, the stem grows upwards and the roots grow downwards. A pot of water is buried in the soil next to the plant on the right. The roots of this plant have curved around to grow towards the water.

Shown is a colour photograph of bean plants with tendrils wrapping around wooden poles.

Most of the frame is filled with bean plants supported by dark brown wooden poles. The plants are thick with wide green leaves. The plant in the foreground is in sharp focus. Its tendrils are thin, pale green and thread-like with smaller growths that curl like corkscrews. The tendrils wind tightly around the pole from the main plant up to the top of the picture.

Shown is a colour illustration of 5 grass seedlings, altered as they would have been in Charles and Francis Darwin's experiments.

Across the top of the illustration, the sun is represented by a thick, pale yellow stripe, with a bright yellow half-circle on the left side. Near the bottom, a long brown rectangle represents the soil. The roots of each seedling grow downwards in the rectangle. Above the soil, each seedling is about the same size, with a long, pointed structure that becomes darker green near the tip. These are labelled Coleoptile with a black arrow. 

The first coleoptile curves left, towards the sun. No alterations are visible on this seedling.

The tip of the second coleoptile has been cut off. This seedling grows straight up, with no curve.

The tip of the third coleoptile is covered with black material. This seedling also grows straight up, with no curve.

The tip of the fourth coleoptile is covered with transparent material. It curves to the left, towards the sun.

The base of the fifth coleoptile, below the tip, is covered in black material. This seedling also curves left, towards the sun.

Shown is a colour illustration of two grass seedlings, altered as they would have been in Peter Boysen-Jensen's experiments.

Across the top of the illustration, the sun is represented by a thick, pale yellow stripe with a bright yellow half-circle on the left end. Near the bottom, the soil is represented by a dark brown rectangle. The roots of both seedlings grow downwards in the rectangle. Above the soil, both coleoptiles are about the same size. 

On the left coleoptile, the tip is separated from the rest of the seedling by a square of grey material. This is labelled Gelatine, with a black arrow. This tip curves to the left, towards the sun.

On the right coleoptile, the tip is separated from the rest of the plant by a square of black material. This is labelled Piece of rock, with a black arrow. This tip points straight up, with no curve.