20 



MOVEMENTS OF CURVATURE 



chains of cells are also capable of spontaneous movement, as is shown by 

 the stolons of Mucor stolonifcr, as well as by Spirogyra and other Con- 

 jugatae. The threads of Spirogyra may often curve into rings or spirals, 

 and subsequently straighten themselves. As in the case of growth in 

 length, periods of rest and of activity alternate, and during the latter, curva- 

 ture may appear in a few minutes, and a complete circle be formed in ten 

 minutes to half an hour *. In connexion with its peculiar mode of growth, 

 lateral bending may be produced in the filaments of Oedogoniitm, pre- 

 sumably because the cell-wall splits and the ring 

 of plastic cellulose stretches sooner on one side i 1 



than on the other. 



All stages are shown between trifling and 

 pronounced nutation, according to the plant, to 

 the stage of development, and to the external 

 conditions. The curves are not always regular 

 and similar, even when there is a pronounced 

 tendency to linear, elliptical, or circular nodding, 

 as the case may be. Even when the last named 

 is most pronounced it may temporarily alter into 

 to-and-fro pendulum movements. Slight circum- 



FIG. i. Nutation of the sheathing leaf of 

 the seedling of Zea Mays, from 8.30 a.m. on 

 Feb. 4 to 8 a.m. on Feb. 6. The movement 

 is magnified 25 times. (.After Darwin.) 



FlG. 3. Circumnutation of a cotyledon 

 of Lagenaria viilgaris i inches long, 

 from 7.35 a.m. July n to 9.5 a.m. July 14. 

 Magnified 8 times. (After Darwin.) 



nutation may change to a single large circular or lateral movement, 

 although a very irregular curve is produced when the movement of the 



Ber. d. hot. Ges., 1902, pp. 526, 580; Neubert, Jahrb. f. wiss. Bot., 1902, Bd. xxxvin, p. 149 

 (Allium) Richter, Ber. d. bot. Ges., 1903, p. 175 (Seedlings). 



1 The movements of Zygnemaceae were known to Link, Grundlehren d. Anatom. und Physiol., 

 1807, p. 263; Meyen, Pflanzenphysiol., 1839, Bd. in, p. 567; and were studied in detail by 

 Ilofmeister, Jahreshefte d. Vereins f. vaterland. Naturkunde in Wiirttemberg, 1874, Bd. xxx, p. 211, 

 and Oltmanns, Flora, 1892, p. 199. That they occur under constant conditions has been shown 

 by Winkler, Kriimmungsbewegungen von Spirogyra, 1902, who also found that when suddenly 

 killed the curvatures were retained. To show the movement single threads may be observed in white 

 porcelain dishes. 



