Page 126 - Photosynthesis: The Green Miracle

Internal hydraulic pressure
in plants is exceedingly
important. The potted plant
at left has not been wa-
tered, and its cellular pres-
sure has fallen to zero.
However, 30 minutes after
being watered the same
plant has re-acquired inter-
nal pressure and resumed
the appearance shown in
the photo below.

Pulvinus

Sap

Cells retaining
turgor
1

Pulvinus
Cells losing turgor
Venous tissue
2 3

1. Pulvinus: supports projecting underneath the leaf
2. Pulvinus cross-section: state of cells before the plant is disturbed
3. Pulvinus cross-section; turgor loss and leaf fall