THE COVERING TISSUES 95 



(c) Branching; 



non-branched — branched. 



(d) Arrangement of cells; 



uniseriate — multiseriate . 



Unicellular hairs consist of but one cell, whereas multi- 

 cellular hairs consist of many cells. If but one hair 

 originates from an epidermal cell it is termed a simple 

 hair, as distinguished from a compound hair in which 

 several trichomes have their origin in one epidermal 

 cell. The terms branched and non-branched are self- 

 explanatory; but the distinction between compound 

 and branched trichomes must be kept clearly in mind. 

 Branched forms differ from compound forms in that 

 the former project from the epidermal cell as a single 

 hair, and the branching occurs at some point above 

 the origin. Uniseriate trichomes are multicellular 

 forms in which the several cells composing the hair 

 are arranged in a single row or series. Multiseriate 

 trichomes are likewise multicellular, but the cells com- 

 posing the hair are arranged in several parallel rows 

 or series. In describing plant hairs the four points 

 enumerated above must be taken into consideration. 

 The hairs of cannabis and senna are unicellular, 

 simple and non-branched. The hairs of digitalis and 

 matico are multicellular, simple, non-branched and 

 uniseriate. The hairs of althaea leaves are unicellular, 

 compound and non-branched. Among the several 

 kinds of hairs present in arnica flowers, we find multi- 

 cellular, simple, non-branched and multiseriate types. 

 Mullein leaf possesses simple, multicellular, branched, 

 uniseriate trichomes. The various types of trichomes 

 are illustrated in Plates 35, 36 and 37. 



The cells of non-glandular trichomes often show 



