ON THE HAIRS AND CUTICLE OF LABRADOR TEA LEAVES. A DEVELOPMENTAL STUDY

Publisher Website
Google Scholar
Abstract
Developing buds of Ledum groenlandicum Oeder. are studied. By the latter part of May, those that will produce next year's leaves are well advanced, and a month later beginnings of epidermal hairs are present on the leaves. The morphological development of the hairs is traced. Elongate hairs, both multicellular and unicellular, have long, cylindrical, or semicylindrical, vacuolate cells. The elongating cells have a transverse orientation of the cellulose microfibrils in their primary walls as demonstrated by the polarizing microscope. The vacuolate cells of capitate hairs do not become cylindrical, and they lack the regular orientation of the cellulose in their walls. The pectic material does not become calcified, and the hardening of this part of the wall is thus eliminated as a factor in shape control. The abscission of hairs from the upper leaf surface is brought about by a softening of the middle lamella, apparently through a change from pectic acid to soluble pectin rather than by depolymerization. The hairs on the lower surface remain attached, but the walls of their basal cells become cutinized and the hairs are thus isolated from the leaf tissues. An incipient cuticle covers the young leaves in buds collected in November. At this time the linking together of molecules to form cutin has begun, as indicated by the insolubility of the layer in fat solvents, but the bonds must be few, the layer being easily broken down by a solution of sodium hydroxide. The gradually increasing difficulty in bringing about this reaction indicates that, except during the cold of winter, there is a gradual increase in the bonding until late May or early June, when the cuticle is fully formed. Additional evidence was found for the hypothesis that the developing cuticle exerts a deciding influence on the shape of epidermal cells.