Pisum sativum is more commonly known as the pea plant. These plants are well known for growing peas in pods which are the plant’s fruit. This is an important crop now grown in many parts of the world. It is thought that peas were first domesticated in the area of modern day Greece, Turkey and Syria. Despite now being a commonly eaten vegetable, when peas were first introduced to France in the 1600s they were described as a luxurious delicacy. Peas were also vital to the discovery of modern genetics as Gregor Mendel used simple characteristics, such as shape and colour of the pea seeds, to understand inheritance.

The roots of the pea plant have developed from one primary root, which grows downwards  more or less straight. From this primary root, a large number of secondary (or lateral) roots have branched to fill the pot.

How do roots know in which direction to grow? A process called positive gravitropism directs root growth downwards into the soil. The primary root has a strong positive gravitropism which makes it grow down more or less vertically. Lateral roots have a less strong positive gravitropism, so that they grow downwards but also sideways. This allows the plant roots to explore the soil for anchorage, nutrients, and water.

In the ageotropum pea mutant, positive gravitropism does not work. Without gravitropism as the main force for an ordered root (system) structure, the roots are growing randomly through the soil.