CHAP. II. HAIRS. 47 



surface, and diverge a little from their centre, as in the Mal- 

 low tribe. It is hairs of this description that close up the 

 abortive stomates upon the under side of the leaves of Dionsea 

 muscipula. 



Hairs are either formed of a single cell of cellular tissue 

 (Plate I. fig. 8. b), or of several placed end to end in a single 

 series (Plate I. fig. a, b.), whence, if viewed externally, they 

 have the appearance of being divided internally by transverse 

 partitions. They are sometmies branched into two or three 

 forks at the extremity, as in Alyssum, some species of Apar- 

 gia, &c. Occasionally they emit little branches along their 

 whole length : when such branches are very short, the hairs 

 are said to be toothed or toothletted, as in the fruit of Torilis 

 Anthriscus; when they are sometliing longer, the hairs are 

 called branched, as in the petioles of the gooseberry ; if longer 

 and finer still, the term is pinnate, as in Hieracium Pilosella; 

 if the branches are themselves pinnate, as in Hieracium undu- 

 latum, the hairs are then said to be plumose. It sometimes 

 happens that little branchlets are produced op one side only 

 of a hair, as on the leaves of Siegesbeckia orientalis, in which 

 case the hair is called one-sided (seaindatus) ; very rarely they 

 appear upon the articulations of the hair, which in that case is 

 called ganglioneous. (Plate I. fig. 9. Verbascum Lychnitis) : 

 the poils en goupillon of De Candolle are referable to this form. 

 Besides these, there are many other modifications : hairs are 

 conical, cylindrical, or moniliform, thickened slightly at the 

 articulations (tondose), as in Lamium album, or much en- 

 larged at the same point {nodulose), as in the calyx of Achy- 

 ranthes lappacea. 



Hairs are sometimes said to be Jixed by their middle 

 (Plate I. fig. 10. c); a remarkable structure, common to many 

 different genera ; as Capsella, Malpighia, Indigofera, &c. 

 This expression, however, like many others commonly used 

 in botany, conveys a false idea of the real structure of such 

 hairs. They are in reality formed by an elevation of one 

 bladder of the cuticle above the level of the rest, and by the 

 developement of a simple hair from its two opposite sides. 

 Such would be more correctly named divaricating hairs. 



