Abstract/Summary:
The trichomes consist of basal-, stalk-, and apical cell. The cuticle proper is lamellate, but extremely thin on apical cells. Exposed walls of stalk cells and the sunken basal cells develop thick cuticular layers. A lamellate suberin wall is deposited all over the inner surface of the mature stalk cells, cutting off plasmodesmata. Then the apical cells are shed. This happens when repeated hygroscopic spiralizing and despiralizing cause brittleness in the wall between the apical cell and the stalk cell. The trichomes develop before differentiation of stomata begins. The primary function of the indumentum is to enhance the transpiration stream, thereby securing sufficient mineral supply for rapid leaf growth. Secondary, the indumentum may protect against high insolation during leaf growth. Although the hairs are dead on mature leaves, they are of no value in reducing transpiration due to a wide spacing. Therefore the apical cells can be shed early. Trichomes with tannin-storing apical cells were observed mainly in the axils of young leaves. Possible ultrastructural differences between lamellate cutin and suberin walls are discussed.