62 
ORGANOGRAPHY. 
BOOK 1. 
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 two principal 
kinds of hairs; viz. the Lymphatic and the Secreting. Of 
these, lymphatic hairs consist of tissue either tapering gradu- 
ally from the base to the apex, or at least not much enlarged 
at either end; 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 instance. When a 
O 
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 portion of 
the stem that is formed under ground, nor upon any parts 
that grow under water. 
In a very large number of hairs, perhaps in all, there may 
be seen, at some period of their existence in any cell, a cyto- 
blast, and a circulating system, formed of numerous fine 
streams, which all appear to proceed from and return to the 
cytoblast itself. (See Plate II. fig. 13. 14. 18.) In the monili- 
form disarticulating hairs of Polystachya, already described, 
each joint of the hair has this structure in a very remarkable 
manner. 
If hairs are examined with low magnifying powers, their 
sides appear to be simple, and they are accordingly regarded 
as mere expansions or attenuations of the vesicles of the 
epidermis : but if they are studied with more attention and 
more powerful microscope, it becomes evident that their sides 
are double; for currents may often be seen streaming along 
their sides, and evidently interposed between the external 
