Leaf base is swollen to form A in some B.

In some leguminous plants the leafbase may become swollen, which is called the pulvinus. It is present at the apex or base of the petiole.

The swelling results due to change in the turgor pressure. Night closure movement of legume leaves shows this pulvinar movement. The pulvinus protects the young axillary bud. they are autonomous organs, which perform induced movements also when, detached from stem and leaf. Anatomically all pulvini consist of thick-walled water conducting vascular tissue surrounded by thin-walled motor cells which can undergo visible swelling and shrinking. Pulvinus-based leaf movements occur in many plants of the bean family (Fabaceae), the fastest responses can be found in Mimosa pudica. While most plants can move their leaves only up and down, lupines move them in any direction.