178 



inately connected with tlie geotropic-stimnhis botli of the stalk and 

 of the ovaiy, while the "rectipetaiity" sliould also play a part it. 



VöcHTiNQ gave the name of "rectipetaiity" to the plienometion 

 that a plant-organ, which has curved upon irritation, begins straight- 

 ening itself out again as soon as the stimulation has ceased. This 

 he regards as a separate quality of plant-organs since it further 

 appeared that the straightening required no new stimidation. It 

 seems to me, however, as I set forth also in my article quoted 

 above, tliat rectipetaiity must be regarded ratliei' as a consequence 

 of the original stimulation which, being gradually conducted to the 

 opposite side of the organ, causes a contrary curving. 



In Papaver the young flowerbud stands upright on a short and 

 vertical peduncle; soon, however, the rapidly growing stalk makes 

 a curve of 180°, so that the bud now hangs inverted. In this 

 position the peduncle continues to grow which takes place at the 

 bend, without however the curve increasing, owing to the simul- 

 taneous tendency towards rectipetaiity, and so it seems as if the 

 growth is limited entirely to the part below the bend. When the 

 flower is fully formed, the bud rises again and this upright position 

 is also retained by the fruit. 



Amputation of the ovary only (inside the bud before it is full- 

 grown) checks the growth of the stem, which then stretches straight 

 out as much as possible; the cessation in the growth should be 

 regarded as a result of the cessation of the gravitation-stimulus in 

 the ovary, the straightening of the stalk as caused by the "rectipe- 

 taiity" which is then the result of the stimulus received before the 

 ovary was cut off. 



The peduncle as well as the bud is negatively geotropic; the 

 static apparatus should thus again be supposed to lie against the 

 basal transverse wall and this position should remain unchanged in tlie 

 peduncle. The reason that the growing stalk bends over at an angle 

 of 180° should be attributed to a shifting of the static apparatus in 

 the slatocysts of the ovary from the lowest transverse wall to the 

 uppermost, while the erecting of the full-grown bud later on should 

 be preceded by the opposite movement in the same cells. 



This example shows well how simply these seemingly complicated 

 movements can be explained upon our assumptions. 



A last group will comprise the epinastic and hyponastic movements 

 which are so common in plagiotropic organs. 



These movements depend upon temporary inequalities in the speed 

 of growth between the upper and lower surface of the organ 

 (especially leaves), whereby the growth predominates now on one 



