TTLA-3Epidermis

The Acquisition, Translocation & Retention of Water are the most critical problems confronting Land Plants.

Translocation of Photosynthate is also Vital!

Several Major Classes of Vegetative Adaptations led to the Conquest of the Land.

These involve the Epidermis, Ground Tissues & Vascular Tissues.

Epidermis

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 have Rhizoids which are produced by the Epidermis.

Fern Gametophyte with hair-like Rhizoids
(lower right).

Root Hairs are an important Epidermal adaptation.

Hairs can Secrete substances to the surface.

Gynoecium with other floral parts removed. Note the Nectar near the base of the Ovary.

Nectaries are the most important Epidermal secretory structures. These attract Pollinators and Defenders.

Flowering plants have developed highly specific interrelationships with pollinators which assure successful sexual reproduction. Pollinators usually visit flowers to collect Nectar.

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.

Roots are specialized to absorb water from the soil.

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.

The Anthophyta are the only plant division that produces many kinds of Epidermal Hairs!
The Pterophyta produce a smaller variety of Scales and Hairs.