182 



direction. It appears to me that these movements may also he 

 explained by an anionomons siiifting of the static apparatus. We 

 have seen (page 0) thai the tip of the young stem which at tirst 

 is vertical soon afiervvat'ds assumes an almost horizontal position, 

 after which it begins to twine; this was then explained bj a shift- 

 ing of the apparatus from tiie basal transverse wall to one of the 

 longitudinal vvalLs which then by the bending became the lowest. 

 And if this apparatus were displaced now again in the statocyst, 

 so that it goes round the cell, but always keeping at one of the 

 longitudinal walls, this would cause the tip twisting aback and at 

 the same time its rotating in the horizontal plane, since this twisting 

 coiihl not take place without a siiniillaneous and equally rapid 

 rotation (one tuin for each circle described in the horizontal plane). 

 This displacement should take place in the one direction in plants 

 which twine to the left and in the opposite direction in plants 

 which twine to the right. If the summit of the stem is not perfectly 

 horizontal in rotating as often occurs, the apparatus should have 

 to lie still at the longitudinal wall but somewhat shifted towards 

 the basal transverse wall aiui should be carried round in this same 

 position in the cell. 



It is woi'th noting in this connection that this displacement of the 

 apparatus, and also the nature of the mo\ement of the stem, agree 

 largely with those described for the rotating nutation above-mentioned; 

 for this reason, and because, in our opinion, both are to be regarded 

 as dependent upon the gravitation-stimulus, the old supposition of 

 Sachs is confirmed again, viz. that twining and rotating nutation are 

 movements intimately connected with each other. The only ditïer- 

 ence would consist in the size of the apical angle of the cone 

 described by the tip of the stem (which in twining plants may be 

 as much as 180°) and thus, with regard to the static apparatus, 

 in the distance, which exists continually during the shifting between 

 the middle-lield and the centre of the basal transverse wall. 



This discussion, though necessarily too short, may however suflice 

 to show that with the hel|) of oiii' theory it is possible to give even 

 a simple explanation of the lateral geotropism. 



A siiifting of the apparatus back to the original position at the 

 basal transverse wall would again lead to the negative geotropism 

 wich causes the stem to raise itself when the twining ceases and 

 by which the convolutions are pressed against the support. 



The twisting of the stem which can frequently be observed as 

 an accompanying phenomenon and which probably also depends upon 

 the gravitation, cannot be discussed here. 



