THE DEVELOPMENT OF THE PELTATE HAIRS OF SHEPHERDIA CANADENSIS

Abstract

It is well known that the characteristic silvery or reddish-brown appearance of the young twigs, buds, and leaves of the members of the Elaeagnaceae is due to a thick coating of peltate and stellate hairs. An examination of three members of this family, Shepherdia canadensis (L.) Nutt., S. argentea Nutt., and Elaea gnus angustifolia L. has shown the peltate hairs to be almost constant in size and shape within each species and very similar for the species examined. The peltate hair may be described as consisting of a central stalk bearing a flattened or conical shield. The shield is made up of a considerable number of ray cells which usually have somewhat thickened walls and empty cell cavities. The distal end of each of these ray cells is free and tapers to a point. It has been suggested by earlier investigators that the presence or absence of peltate hairs, and, if present, the form, size, and color of such hairs could be used in distinguishing between genera and species of plants. Schacht (I852, I856) found that the scales (Schuppen) of the Elaeagnaceae were very similar to those of the Bromeliaceae. Prillieux (I856) separated some 23 members of the Oleaceae on the basis of the type of star hairs (poils en etoile) characterizing each species. He found that the hairs differ in size, shape, and color, and in the number of cells in the shield. He considered the peltate hair to be actually a stellate hair, in which the radiating cells of the shield are held together by a cuticle. De Candolle (I856) used the presence and form of the peltate hairs (radiotca pilosae) as taxonomic characters in describing the members of the Elaeagnaceae. Vesque (I882) made use of various types of peltate hairs (poils en e'cusson), stellate hairs (poils en e'toile) and bunched hairs (poils en pinceau) as taxonomic characters in the Capparidaceae. Haberlandt (I884) described the scale hair (Schuppenhaar) as characteristic of members of the Elaeagnaceae. According to Bachmann (i886), Radlkofer (I884) observed a similarity in the structure of the peltate hairs of the members of four families of plants. Bachmann (i886) studied the peltate hairs (Schildhaaren) and the stellate hairs (Sternhaaren) of some 34 families of Angiosperms. On the basis of the characters of the peltate hairs, he formed a key to the genera of the