MORPHOLOGY 



107 



FIG. 117. Glandular hair from 

 the petiole of Primula sinensis. 

 (After DE BARY, x 142.) 



which, especially in the case of some tropical nettles, may cause 



severe inflammation. 



The cells surrounding the base of a hair are often arranged in 



a ring or in radiating lines, or are otherwise different from the 



surrounding epidermal cells. Such cells may 



be called subsidiary cells to the hairs. 



UNICELLULAR HAIRS, such as we have 



so far considered, may terminate in well- 

 defined heads resulting from the swelling of 



their tips, or their side walls may develop 



irregular excrescences ; on the other hand, 



they may remain short and expanded like a 



balloon, or remain close to the surface of 



the epidermis as spindle-shaped or stellate 



hairs. MuLTlCELLULAR HAIRS may be 



merely simple rows of similar cells, as the 



hairs on the stamens of Tradescantia (Fig. 



60) ; or their terminal cells may become 



swollen into globular heads (Fig. 117), like 



those on the Chinese Primrose (Primula 



sinensis) ; or an epidermis may be covered 



with disc-, star-, or bowl-shaped hairs (Fig. 118). Sometimes the 



hairs become variously branched, lose their living contents, and form 



a silky or woolly protective covering similar to that formed by uni- 

 cellular hairs. In special cases, as in the 

 scale hairs of Ferns, they may even have 

 the shape of a small leaf. 



EMERGENCES, unlike hairs, are not 

 formed solely by epidermal cells, but a 

 number of cells, lying more or less deeply 

 in the sub-epidermal tissues, also take part 

 in their formation. Thus, for example, 

 while only a few rows of sub-epidermal cells 

 enter into the formation of the emergences 



FIG. 118,-Gianduiar scale from the (Fig. 119) on the margins of the stipules of 

 female inflorescence of the Hop, the Pansy (Viola tricolor}, much deeper- lying 



Humvlus Lupulus, in vertical tisgue participates in the development of 



section. A, before, B, after the 



cuticle has become distended by the emergences which, as PRICKLES, serve 

 the excretion, in B the ex- j n t ne case o f Roses as a means of protection, 



cretion has been removed by j ,1 , r . , 



alcohol. (After DE BARY, x H2) and at the same tim e are of assistance in 

 climbing. The thick emergences, which 



spring from the roots of the Podostemaceae, and serve to attach 

 them to rocks, are parenchymatous throughout, but vascular bundles 

 may be included within emergences, as is well shown in the club- 

 shaped digestive glands or tentacles (Fig. 120) on the leaves of the 

 Sundew (Drosera). Some emergences resemble in structure certain 



