644 CONSERVATIVE ORGANS. [t,ECT. XI. 



almost always solid. The term comprehends two 

 species of bristles: the forked and the fasciculated. 



1. Forked bristles (setcefurcatce) are, in some 

 instances, merely rigid, hairlike bodies terminating 

 in two or three diverging points (Plate 9, fig. 23, 

 24), as in Thrincia hispida; but in other cases, as, 

 for instance, on the stems and leaves of the Hop 

 plant, Humulus lupulus, the stalk of the bristle, 

 which is supported on a firm cellular tubercle, is 

 very short, and its forking extremities resemble 

 two flattish, awl-shaped bristles (Plate 9, fig. 25) 

 pointing in opposite directions. 



2. Fasciculated bristles (setce fasciculatce) con- 

 sist of a number of simple straight bristles diverg- 

 ing from a papillary knob, as in Cactus flageUi- 



formis (Plate 9, fig. 26). 



There is still another species of pubescence 

 that cannot properly be arranged with any of those 

 which have been described; it is found on a spe- 

 cies of Houseleek, Sempervivum arachnoideum, 

 extending like a very fine thread, stretching from 

 the tip of one leaf to that of another, and resem- 

 bling so exactly a spider's web, that the plant 

 has been named arachnoideum. 



The pubescence of plants is liable to be af- 

 fected by climate, soil, culture, and other circum- 

 stances: thus, to mention a few only of these 

 changes, Sweet-scented Woodruff, Asperula odo- 

 rafa, is villous, or covered with shaggy hairs, when 

 it grows in the shade, and scabrous when in ex- 



