MOVEMENTS OF IRRITATION. 491 



rotating nutation is a resultant movement brought about by the co- 

 operation of two factors (spontaneous nutation and negative geotro- 

 pism), to experiment with the help of the clinostat. The apparatus 

 is set up on a vibration-free table, and we work with pot plants of 

 Phuseolus or plants of Ipomo?a chrysantha raised from seed. We 

 fix tlu' lower part of the plant, which has so far been free from sup- 

 port, to a suitable stick standing in the soil of the culture vessel, so 

 that only the summit of the shoot to a length of a few centimetres 

 remains free. This shoot end must be very vigorous in develop- 

 ment, and must not bend much by its own weight when the plant 

 is placed in the horizontal position. In this horizontal position a 

 Hank-curvature (preliminary curvature) now very soon appears in 

 the originally straight shoot end. If the plant is now transferred 

 to the clinostat, and set in slow rotation in the vertical plane (it 

 is sufficient if the clinostat is so adjusted that one complete revo- 

 lution is effected in about ten minutes, see 176), the preliminary 

 curvature soon disappears again, being compensated by processes 

 of growth, and the shoot becomes straight. New nutations, how- 

 ever, arise, which are again compensated or remain more or less 

 persistent. The shoot has therefore an internal tendency to move- 

 ments of nutation. When rotating on the clinostat, however, 

 since the effect of gravity is eliminated, rotating nutation cannot 

 take place, but only an undulating nutation. The power of the 

 shoot to perform spontaneous nutations is a necessary prior condi- 

 tion for the production of flank-curvatures, which as we saw act as 

 horizontal components in rotating nutation. This latter is there- 

 fore the resultant of two factors of the spontaneous "nutation of 

 the shoots, and of their negative geotropic movements. 



The clinostat experiments are to be continued, if possible, for a 

 good time, so that we may satisfy ourselves by accurate observa- 

 tion of the behaviour of the plants that rotating nutation does not 

 take place. Then it is convenient to use for the support a glass tube 

 about 1 cm. in diameter, standing in the soil of the culture vessel, 

 and slip into it a number of successively smaller glass tubes. 

 These we draw out as the shoot grows, in order that with increas- 

 ing length it may always be conveniently fixed, while only its 

 actively growing terminal portion is ever free. 



1 Baranetzki, Memoires de Vacad. imper. de St. Petersbourg, Ser. vii., T. 31, 

 No. 8, 1883. 



2 Wortmanu, Botan. Zeitung, 1886. 



