38 THE RQOTl PART I. 



SUBSECTION V. 



The Tuberous Root. The tuberous root (PL I. 

 Fig. 5.) is a root consisting of a knob or tubercle fur- 

 nished with a number of small and scattered fibres ; 

 or of a number of knobs or tubercles united by 

 means of such fibres, and forming a cluster. If the 

 knob is single it is generally of a spherical form, as 

 in the Earth-nut, Bunium Bulbocastanum, and 

 Arum maculatum ; though in some cases the knob, 

 when it attains to its full growth, becomes hollow 

 as in that of Fumaria cava. 



Itsvarie- But of roots consisting of more than one knob 

 there is a considerable variety. Sometimes the 

 knobs are in pairs, as in the root of the Ophrys 

 spiraliS) or Ladies' Traces, and of the early Purple 

 Orchis. If a pair of these knobs is taken and sepa- 

 rated and then immersed in water, the one will be 

 found to sink and the other to swim. This is a 

 phenomenon that seems also to have puzzled the 

 simplists of antiquity not a little ; and to have given 

 rise to a great deal of idle and superstitious con- 

 jecture. It was thought that the knob that swims 

 must necessarily have possessed some peculiar and 

 potent properties, and accordingly some potent 

 properties were very liberally ascribed to it. If 

 prepared in a particular manner and worn about any 

 one's person, it was believed to have the singular 

 property of exciting, by means of proper manage-. 



