more on the ventral (lower) surface of the leaf. This means that less water vapour is
lost because the ventral side of the leaf is in the shade and therefore does not get as
hot.
- Sunken stomata: some plants such as xerophytes have sunken stomata as a way of
preventing water loss. Xerophytes (pronounced ”zero-phytes”) are plants that are nor-
mally found in hot, dry areas such as deserts. The sunken stomata creates a small
pocket of moist air. The high humidity in the air pocket reduces the water potential
gradient between the leaf air spaces and the exterior, and therefore decreases the rate
of transpiration.
Figure 6.21: Sunken stomata.
- Thickened cuticle: Some plants that occur in dry places have a thick cuticle that re-
duces transpiration.
Figure 6.22: Desert plants like cactus have thick cuticles to avoid water loss.
- Hairs on leaves:Hairs trap a small layer of water that works in three ways to reduce
transpiration: (i) creates a pocket of moist air to reduce the water potential gradient,
(ii) increases the sheen on leaves to make them more reflective. The combination of (i)
and (ii) result in a cooling effect that also decreases transpiration.
Figure 6.23: Hairy leaves to trap water
- Reduction of leaf size: Small leaves have a smaller surface area for transpiration to
occur.
- Leaf spines: Some plants have spines instead of leaves. Spines usually have thicker
cuticles and a very small surface area, which decreases transpiration.
Chapter 6. Support and transport systems in plants 177
