48 ORGANOGRAPHY. BOOK J. 



Wlicii the central bladder has an unusual size, as in Mal- 

 pighia, these hairs are called j^oils en navette {pill Malpighiacei) 

 by De Candolle, and when the central bladder is not very 

 apparent, />o^75 en fausse navette {pili ' Jjseudo-Maljnghiacei, 

 hiacumiuati), as in Indigofera, Astragalus asper, &c. In 

 many plants the hairs grow in clustei's, as in Malvaceae, and 

 are occasionally united at their base : such are called stellate^ 

 and are frequently peculiar to certain natural orders. (Plate I. 

 fig. 10. a.) 



All these varieties belong to one or other of the two princi- 

 pal kinds of hairs ; viz. the Lymphatic and the Secreting. Of 

 these, lymphatic hairs consist of tissue tapering gradually from 

 the base to the apex; and secreting^ of cellules visibly distended 

 either at the apex or base into receptacles of fluid. Mal- 

 pighiaceous and glandular hairs, stings, and those which cause 

 asperity on the surface of any thing, belong to the latter; 

 almost all the other varieties to the former. 



When hairs arise from one surface only of any of the 

 appendages of the axis, it is almost always from the under 

 surface; but the seed leaves of the nettle, and the common 

 leaves of Passerina hirsuta, are mentioned by De Candolle as 

 exceptions to this rule : certain states of Rosa canina might 

 also be mentioned as exliibiting a similar phenomenon. When 

 a portion only of the surface of any thing is covered by hairs, 

 that portion is uniformly the ribs or veins. According to 

 De Candolle, hairs are not found either upon true roots, ex- 

 cept at the moment of germination, nor upon any part of the 

 stem that is formed under ground, nor upon any parts that 

 grow under water. 



4. Of Scurfiness. 



ScuRFiNESS consists of thin flat membranous processes, 

 formed of cellular tissue springing from the cuticle. They 

 may be considered as hairs of a higher order, — as organs of 

 the same nature, but more developed ; for they differ from 

 hairs only in their degree of composition. They are of two 

 kinds, Scurfs properly so called, and liamenta. 



Scurfs, properly so called, are the small, roundish, flattened, 



