angle from the preceding stem.

Ravenalasgrowing between two buildings inKinshasa,Democratic Republic of Congo. The plane (here perpendicular to the north-south axis) of these two plants is orientated to maximize daylight absorption.

Phototropismis the growth of an organism in response to a light stimulus. Phototropism is most often observed inplants, but can also occur in other organisms such asfungi. The cells on the plant that are farthest from the light have a chemical calledauxinthat reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many planttropismsor movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism (skototropism).[1]Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth.[2][3]Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them. The combination of phototropism and gravitropism allow plants to grow in the correct direction.[4]

Demonstration of phototropismA young seedling is grown in a phototropic chamber. It consists of a tight box. It has a-removable- lid. Its inner side is painted black. It has a glass window one side. Therefore, light can enter only from this side. Phototrophic behaviour is studied on coloured screens. It shows that the maximum phototropic effect is produced in the blue violet end of the spectrum and the least in the yellow rays.