156 MODIFICATIONS OF HAIRS. [BOOK i. 



Throughout the whole length of the cell the coils are nearly 

 contiguous ; in the lower part they are united by connecting 

 fibrils, and towards the base of the adherent portion become 

 completely reticulated. The testa is a semi-transparent 

 membrane formed of nearly regular hexagonal cells, whose 

 centre is occupied by an opaque mass of grumous matter. 

 Those cells which surround the bases of the hairs are consi- 

 derably elongated, and, gradually tapering into transparent 

 tubes, appear to occupy the interior of the spiral clusters. 

 Two species of Blepharis are mentioned as possessing a struc- 

 ture very similar to that of Acanthodium, differing chiefly in 

 the smaller and more uniform diameter of the tubular spiral 

 cells, and in their thicker fibre, which is always single and 

 loosely coiled. The seed of Ruellia formosa on being placed 

 in water, develops from every part of its surface single short 

 thick tapering tubes, within which in some case a spiral fibre 

 is loosely coiled, whilst in others the place of the spiral fibre 

 is supplied by distant rings. 



In the seeds of Ruellia littoralis, Phaylopsis glutinosa and 

 Barleria noctiflora, the whole surface becomes covered with 

 separate tubes, very similar in form, but destitute of spiral 

 fibre, and terminating in a minute pore, from which streams 

 of mucilage are discharged. (Linn. Trans, xix. 65.) 



Very singular hooked hairs are described by the same 

 author in the same place. 



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 gra- 

 dually 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 some peculiar 

 fluid. Malpighiaceous 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 



