EIGHT-HAND AND LEFT-HAND CONTORTION. 



471 



Fig. 2. 



north or south. Linnaeus has provided, however, that you are 

 to look south. Similarly, when you have entered the circle, the 

 direction of motion will be reversed if you stand upon your head ; 

 not because you entered the circle, but because you stood upon 

 your head. Tou may stand on your head without entering the 

 circle. Linnaeus did not provide against this ; it is, however, 

 the exact point that botanists now have to provide against. 



I have treated the subject for simplicity in one plane ; i. e. I 

 have considered the case of a circle instead of a helix : the latter 

 is really included in the former ; but without talking of projec- 

 tions, we can see that if the circle is cracked at one point and 

 one end lifted up a very little, so as to transform the circle into a 

 very depressed helix of one turn, all that has been stated about 

 the direction of twist in a circle must apply to the twist in the 

 helix ; and it is equally clear that what is true of the depressed 

 helix must be true of a more elongate one. 



J?ig. 2 is intended to show the appli- 

 cation to a contorted corolla, which is 

 represented cut at right angles in two 

 pieces, the upper piece lifted upwards a 

 little. Looking at this upper piece, 

 whether we imagine ourselves within or 

 without, the contortion is dextrorse ; but 

 if we were to take up the lower half of 

 the corolla and look at the section, the 

 contortion would appear sinistrorse : this 

 we may see by looking through the back 

 of the page at the section of the upper 

 half. This is the point at issue between 

 A. DeCandolle and Bentham : A. DeCan- 

 dolle looks down the axis of the flower, 

 Bentham looks up it. In describing a 

 twist there are two points to be settled 

 conventionally: (1) which way round is 

 to be called right-handed ; (2) which di- 

 rection of the axis (round which the twist 

 takes place) is to be reckoned positive. As I understand, there 

 no difference among botanists regarding the first point ; the con- 

 tention is really regarding the second. Bentham takes the axis 

 of vegetative growth as the positive direction ; A. DeCandolle 

 takes that direction as negative, which seems less philosophical ; 



