TTLA-3Epidermis

Invasion Land-Air
Epidermis

The Acquisition, Translocation & Retention of Water are the most critical problems confronting Land Plants. Translocation of Photosynthate (Sucrose) is also Vital! *All of these involve WATER!* Several Major types of Vegetative Adaptations led to the Conquest of the Land/Air. These involve the Epidermis, Ground Tissues & Vascular Tissues.
Many Epidermal Adaptations are crucial for survival in the atmosphere. The Cuticle & Stomata are the most important of these. Hairs or Trichomes are also significant but not absolutely required for survival. Important Trichomes include Rhizoids & Root Hairs. Ancestral organisms like *Marchantia* (Hepatophyta) have Rhizoids which are produced by the Epidermis. Fern Gametophyte with hair-like Rhizoids (lower right). Root Hairs are a fundamentally important Epidermal adaptation. Hairs can Secrete substances to the surface. Gynoecium with other floral parts removed. Note the Nectar secreted near the base of the Ovary. *The Anthophyta* are the only plant division that produces many kinds of Epidermal Hairs, other than Root Hairs & Rhizoids! The Pterophyta produce a smaller variety of Scales and Hairs.**	Note the Thick Cuticle which prevents water loss.! Marchantia thalli - Their shiny appearance is due to a waxy Cuticle. Stomata regulate the movement of water from the leaf & stem. Some hairs deter herbivory! Some hairs capture prey! The complex Glandular hairs of *Drosera* reach the apogee of trichome evolution. An SEM photo which shows that the Epidermis of ohi'a lehua is covered with Trichomes. These create a large "boundary layer" which moderates water loss via transpiration. Cross-section of an Ohi'a lehua leaf viewed with polarized light. The Trichomes are birefringent and appear as bright structures. Note the abundance of Trichomes on the lower surface of the leaf. Stomata are also present on the lower leaf surface. The Trichomes moderate water loss when the stomata are open.
There are many more Epidermal Adaptations. Some cells produce Pigments that protect aerial organs from excess light OR attract Pollinators or Disseminators.
Nectaries are important Epidermal secretory structures. These attract Pollinators and Defenders. Flowering plants have developed highly specific interrelationships with pollinators which assure successful sexual reproduction. However, when pollinaors become extinct, sexual reproduction is severely constrained! This has happened in Hawaii! Pollinators usually visit flowers to collect Nectar or Pollen.

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