LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 659 



this property is so strong, that a piece of dark-co- 

 loured paper placed at the distance of a few inches 

 from them, and changed to different sides of the 

 plant, has the power of altering their direction. 

 The cause of these movements shall be afterwards 

 investigated. 



2. The radicular claw (clavicula radiciformis) 

 is a small cylindrical body, resembling a radicle, 

 which is protruded from the stem ; as exemplified 

 in the Ivy and the Ash-leaved Trumpet-flower, 

 Bignonia radicals. The claws of the Ivy are pro- 

 truded in lines, generally on the side of the stem 

 which is next to the wall on which the plant is 

 supported (fig. 1. p. 250). This is probably owing 

 to the greater moisture and shade on that side 

 being favourable to their formation, as in the case 

 of the real roots *, which appear on a stem by sur- 

 rounding a portion of it with a ball of moist 

 earth ; or of those which protrude spontaneously 

 under peculiar circumstances, as in the case of the 

 Laurel, mentioned in page 197: nor is this opi- 

 nion rendered more problematical by the fact, that 

 the radicular claws are put forth on every side of 

 the old^r stems of the Ivy, giving them a bristled 

 aspect ; for, as in the case of branches and roots, 

 the rudiments of these claws may exist in the 

 stem, although they are not protruded, until cir- 



* I have already noticed (p. 280) the fact, that these claws 

 become perfect roots under certain circumstances. 



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