THE EPIDERMIS AND PERIDERM 



77 



branches, and the walls are rough. Thus the multicellular 

 branched hairs may be divided into subgroups which have 

 alternate, opposite, whorled, or in certain hairs irregularly ar- 

 ranged branches. Each class may be again subdivided accord- 

 ing to color, character of cell termination, etc., as cited at the 

 beginning of the chapter. 



Occasionally multicellular hairs assume the form of a shield 

 (Plate 12, Fig. i); in such cases the hair is termed peltate, as in 

 the non-glandular multicellular hair of shepherdia canadensis. 



Hairs grow out from the surface of the epidermis in a per- 

 pendicular, a parallel, or in an oblique direction. Hairs which 

 grow parallel or oblique to the surface are usually curved, and 

 the outer curved part of the wall is usually thicker than the 

 inner curved wall. 



The mature hairs of some plants consist of dead cells. In 

 other plants the cells forming the hair are living. When dried, 

 those hairs, which were dead before drying, contain air; while 

 those hairs which were living before drying, show great variation 

 in color and in the nature of the cell contents. The contents 

 are either organic or inorganic. The commonest organic con- 

 stituent is dried protoplasm. In cannabis indica are de- 

 posits of calcium carbonate. 



Multicellular multiseriate branched hairs are the ultimate 

 division of the pappus of erigeron, aromatic goldenrod, arnica, 

 grindelia, boneset, and life-everlasting. 



The hairs of erigeron (Plate 13, Figs. 1 and 2) are slender; 

 the walls are porous. Each hair terminates in two cells, which 

 are greatly extended and sharp-pointed; the branches from the 

 basal part of the hairs (Plate 13, Fig. 1) are of about the same 

 length as the apical branches. 



The hairs of aromatic goldenrod (Plate 13, Figs. 3 and 4) are 

 larger than those of erigeron; the diameter is greater and the 

 walls are non-porous. The apex of the hair terminates in a 

 group of about four cells of unequal length, which are sharp- 

 pointed. The branches of the basal cells (Plate 13, Fig. 3) are 

 similar to the branches of the apical cells. 



The hairs of arnica (Plate 14, Figs. 1 and 2) have thick, 

 strongly porous walls; the branches terminate in sharp points. 

 The apex of the hair terminates in a single cell. The basal 



