140 PHYLLOTAXY, OR LEAF- ARRANGEMENT. 



contorted in the opposite direction ; that is, the plaits overlap 

 to the right and are twisted to the left. 1 



261. Direction of Overlapping, &c. This is to be noted in the 

 ternary, quinary, or other forms of spirally disposed imbrication, 

 also in convolute and twisted or contorted aestivation. It 

 may be either to the right (dextrorse) or to the left (sinistrorse) . 

 The application of this term depends upon the assumed position 

 of the observer, whether outside or inside. We always suppose 

 him to stand outside, in front of the object : so when the over- 

 lapping is from right to left of the observer thus placed, as in 

 Fig. 266, it is sinistrorse ; when from his left to right, as in 

 Fig. 267, 268, dextrorse* The direction is generally constant, 

 but in many cases only prevalent, in the same plant or the same 

 species, or even the same genus : sometimes it is uniform or 

 nearly so throughout a whole natural order. 



separately expressed. To describe the aestivation in such cases as dextrorsum 

 contorta et sinistrarsumtorta (or in similar English words), when the overlapping 

 is to the right and the twisting to the left, is at least awkward and cumbrous. 

 Convolute is a fitting name, of occasional early application to this aestivation 

 (as by Jussieu to the petals of Malvaviscus), but without definition in this 

 sense ; it has for many years been steadily adopted by the present writer, 

 is employed by Eichler in Germany, and has recently been adopted by 

 G. Henslow and others in Great Britain. It has, however, the disadvantage 

 of having been used by Linnaeus to express the coiling of single leaves, and 

 in a manner not wholly congruous, but still with one edge outside and the 

 other inside. 



1 In our phraseology, dextrorsely convolute and sinistrorsely contorted ; 

 in the current phraseology above referred to, dextrorsely contorted or twisted 

 and sinistrorsely twisted! 



2 The reasons for adopting this view (in opposition to the authority of 

 Linnaeus and DeCandolle) are given in note on p. 51. 



