48 
ORGANOGRAPHY. 
BOOK I. 
When the central bladder has an unusual size, as in Mal- 
pighia, these hairs are called poils en navette (pili Malpighiacei) 
by De Candolle, and when the central bladder is not very 
apparent, poils en fausse navette (pili pseudo- Malpighiacei, 
biacuminati), as in Indigofera, Astragalus asper, &c. In 
many plants the hairs grow in clusters, 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 exhibiting a similar phenomenon. Wlien 
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. Scurf, properly so called, and Ramenta. 
Scurfs, properly so called, are the small, roundish, flattened, 
