APPENDIX 



APPENDIX C 

 THE USE OF THE TERMS " RIGHT " AND " LEFT " 



These terms are but seldom required in botanic descriptions, being only 

 used to denote the direction of a twist or spiral. Unfortunately they have 

 been employed in opposite senses, so that the meaning of one author may be 

 completely perverted by his misuse of the correct method. In zoology, 

 where bilateral symmetry is common, these terms are always applied to the 

 limbs or organs of an animal with regard to its axis, and the majority of 

 botanists have carried out the same idea with regard to plants. A spiral 

 may be considered as turning to the right or the left, that is, two spirals may 

 run in contrary directions, but the same spiral may be differently designated 

 according to the position of the observer. The orthodox way regards the 

 observer as being placed within while noting the direction of the twist, as if 

 he were looking south, and recording the apparent passage of the sun from 

 his left towards his right ; this, dextrorse, is the common acceptance of 

 "with the sun " or "like the clock hands " ; it is also the motion of driving 

 home a screw, which receives its name of "right-handed " from the motion, 

 and not from the aspect of the pitch of its threads. 



A few observers have disregarded these considerations, and have placed 

 their point of view outside the spiral. The result of this is to reverse the 

 terms, for a dextrorse climbing plant then seems to pass from right to left, 

 which they then term sinistrorse, as the thread of an ordinary right-handed 

 screw when held up for inspection. If we ascend a spiral staircase constantly 

 bearing to our right, we are describing a right-handed spiral, and the stair- 

 case is also dextrorse. Many climbing plants as the Hop and the Honey- 

 suckle take this course, others as the white Convolvulus and Scarlet Runner 

 take the opposite. 



Torsion of the corolla is sometimes highly characteristic, as in some genera 

 of Apocyneae and Myrsineae. It has been recommended that a few words 

 should be added to define the position of the observer, as e centra visum, or 

 externe visum, as the case may be. For a fuller discussion of these points 

 reference should be made to M. Alphonse de Candolle, "La Phytographie," 

 p. 201-208, and Mr C. B. Clarke in the Journal of the Linnean Society, xviii. 

 (1881), 468-473. 



The botanists who have used DEXTRORSE and SINISTRORSE in the sense 

 defined in this Glossary are A. P. de Candolle and his son Alphonse de Candolle, 

 Alexander Braun, G. W. Bischoff, C. R. Darwin, J. C. Doell, W. P. Hiern, 

 J. S. Henslow, H. von Mohl, C. Naegeli and L. H. Palm; those in the 

 contrary sense are G. Bentham, Asa Gray, A. W. Eichler, and Sir J. D. 

 Hooker. Linnaeus's definition is confused by examples, most of which con- 

 tradict his words, while a correction in his "Errata" nullifies the text : see 

 his "Philosophia botanica," 39, 103 note, 310 (1751). 



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