OCCURRENCE AND DISTRIBUTION 23 



the movement of the leaflets of Dcsmodium, Trifolium, or Oxalis until a sufficient 

 pressure has been produced in the pulvinus, and then releasing the leaflet. Similar 

 strains are produced by the growth of the flower-buds of Genista and other 

 Papilionaceae, which finally lead to the sudden opening of the flower *. 



Ephemeral movements. Under constant external conditions the whole 

 progress of development, including the formation of organs, consists of 

 a series of ephemeral movements. Such are all the movements involved in 

 the opening of foliage and flower buds, in the straightening of the arched 

 stems of embryoes, or of the flower stalk of the Poppy, and the fruit stalk 

 of Campanula. In fact, all movements due to autonomic changes in the 

 rate of growth of opposed sides of an organ are of this character. 



In many cases the organ oscillates a few times before assuming a 

 constant position, so that no precise boundary can be laid down between 

 ephemeral and periodic movements. Each stamen 

 of Rnta graveolens (Fig. 5), for instance, after the 

 flower has opened, bends away from the ovary, then 

 applies itself to it, and then again bends outwards 

 towards the perianth. Similarly some flowers open 

 and close more than once, so that in both cases we 

 may term the movements periodic 2 . 



In many cases the older and younger zones 

 of a growing region exhibit dissimilar curvatures. F '9-s- Ruta graveojens. The 



anterior stamens and perianth 



Thus a developing fern frond has a somewhat leaves ", a v e . been Amoved. The 



stamen (a) is pressed against the 



S shape, owing to the fact that the circinately ov^wwiii do the same later on, 



J while (c), whose anther has de- 



coiled apex unrolls by epinastic growth and is 

 carried beyond the position assumed by the adult 

 basal portions. Similarly the stems of etiolated seedlings tfPisnm sativiim 

 and Vicia sativa show wavy curvatures extending over a few internodes, and 

 lying in the same or in different planes. Wiesner terms this 'undulating 

 nutation,' and the lateral displacement of the internodes often produced 

 by the formation and development of lateral buds he calls ' interrupted 

 nutation V The latter may lead to the formation of sympodial stems, but 

 the curvatures themselves are the result of special ephemeral movements. 



1 Cf. Ludwig, Biologic der Pflanzen, 1895, p. 472. 



2 On ephemeral flowers see A. P. de Candolle, Memoires d. savants etrangers de 1'Institut de 

 France, 1806, T. i, p. 338 ; Dutrochet, Memoires, &c., Bruxelles, 1837, p. 238; Royer, Ann. d. sci. 

 nat, 1868, 5 e sen, T. IX, p. 350; Hansgirg, Physiolog. u. phycophytolog. Unters., 1893, p. 163, 

 Beiheft z. Bot. Centralbl., 1902, Bd. xn, p. 268; Oltmanns, Bot. Ztg., 1895, p. 31 ; Schulz, ibid., 

 1902. 



3 Wiesner, Die undulirende Nutation d. Internodien, 1876 (Sep. a. Sitzungsb. d. Wiener Akad., 

 Bd. LXXVil, Abth. i); Bewegungsvermogen, 1881, p. 22; Sitzungsb. d. Wiener Akad., 1883, 

 Bd. LXXXVIII, Abth. i, p. 454. On similar peculiarities in Algae, cf. Nageli, Pflanzenphysiol. 

 Unters., 1855, Heft i, Taf. 5; Berthold, Jahrb. f. wiss. Bot., 1882, Bd. xill, p. 638. See also 

 Goebel, Organography, 1905. 



