RIGHT-HAND AND LEFT-HAND CONTORTION. 469 



the words "e centro visum " or " externe visum." This is rather 

 cumbrous ; but one of the points I hope to make clear in this 

 paper is that it makes no difference whatever whether the de- 

 scriber conceives himself within or without the spire. I hope, 

 therefore, I have already made plain how important it is that 

 botanists, great and small, should employ the term " dextrorsum 

 contortis " in one uniform sense. It is very far from my wish 

 to pretend to decide in which sense, while such divergence in 

 usage reigns among our great men. I do hope in the present 

 paper to clear away much that obscures and confuses the sub- 

 j ect, and to show what the exact and single point is which is in 

 dispute. 



There is no difference of opinion as to which is the right-hand 

 twist; gardeners call it the way of the sun. Both Bentham 

 and A. DeCandolle are agreed that the hands of a clock go round 

 the right-hand way ; we deal at whist and put on the railway- 

 break that way. I do not suppose that in the north temperate 

 zone there is any difference of opinion on this. The employment 

 of the word " dextrorsum " to represent this direction of twist is, 

 however, arbitrary -. the motion is indeed from left to right if you 

 look at the hour 12 in the clock-face or the sun at noon ; but it 

 is from right to left when the clock-hand passes 6 and at the lower 

 (invisible) transit of the sun across the meridian plane. A. De 

 Candolle has remarked this. It only indicates, what requires no 

 mathematics to see, that a twist cannot be completely represented 

 by a linear motion ; one twist must be compared with another 

 twist. In elementary works of mathematics the clock-hand way 

 is taken as the positive direction of a twist, the reverse way as 

 the negative. Mathematicians prefer the term " positive " for 

 the clock-hand way, because it is no more right-hand than left- 

 hand ; but they often slip into the vulgar universal use of the 

 word "right-hand " to describe such direction of twist. There 

 is no reason why botanists should not retain the Linnsean word 

 right-hand for the clock-hand direction, provided it is understood 

 that this use of the word is entirely arbitrary ; if it is maintained 

 that the clock -hand direction is more to the right-hand than to 

 the left-hand, it may become necessary to fall back on the term 

 positive for that direction. 



The botanic definition of right-hand contortion is grounded on 

 the words of Linnaeus — " Sinistrorsum hoc est, quod respicit sinis- 

 trum, si ponas te ipsum in centro constitutum, meridiem adspi- 



