204 PROTOPLASM. 



exposure for ten minutes to a temperature of 49° - 50° in the air 

 before arrest of movement takes place. In Tradescantia hairs 

 the current stops within three minutes upon exposure in air of 

 a temperature of 49°, beginning again when the temperature 

 falls. 



562. The lower limit (minimum) of temperature at which 

 motion taltes place maj' be stated at 0° C, although — 2° has 

 been observed '■ in a single plant, — Nitella sj-ncarpa. 



Until a temperature of at least 15° C. is attained, the move- 

 ment is sluggish. 



563. Sudden changes of temperature have been said by some 

 writers to cause a temporary arrest of the protoplasmic move- 

 ment. Thus de Vries ■' observed that in the root-hairs of Hydro- 

 charis Morsus-ranse tlie protoplasmic current at 21°. 7 C. was so 

 rapid that it passed through one millimeter in 205 seconds ; but 

 upon sudden elevation of temperature to 33° C, 240 seconds 

 were required for it to traverse the same distance. And Hof- 

 meister' found that tlie rapid movement in Nitella flexilis was 

 arrested in two minutes when the specimen was taken from a 

 room at 18°.5 to one at 5°. But, on the other hand, Velten ^ 

 failed to detect such an effect. 



564. At or near the maximum temperature remarkable changes 

 take place in the form of the protoplasmic threads and films. 

 The}' become more or less rounded, although very irregularl}-, 

 and may be completely disintegrated. Such changes have been 

 noted by Max Sehultze ^ at a temperature of about 40° C. in 

 the hairs of Urtica, the stamen-hairs of Tradescantia, and the 

 leaf-cells of Vallisneria. According to Kuhne,° such changes 

 take place within two minutes in the plasmodium of -^thalium 

 septicum (see 540) at a temperature of 39° C. ; the plasmodium 

 of Didymium serpula was affected in the same way at a con- 

 siderably lower point, namelj', 30° C. 



565. When subjected to a temperature lower than the mini- 

 mum for movement, the protoplasmic mass may become disin- 

 tegrated, the solid part separating from a watery portion, which 

 latter may freeze.' If, now, very gradual increments of heat 



1 Botan. Zeitiuig, 1871, p. 723 (Cohn). 



2 Avohiv. Nterlanilaises, v., 1870, p. 385. 



" Die Lelire von der Pflaiizenzelle, 1867, p. 53. 



* Flora, 1876, p. 213. 



' Das Protoplasma d. Rliizopoden iind Pflanzenzellen, 1863, p. 48. 



" tTntersnohungeii iiber das Protoplasma, 1864, p. 87. 



' Untersucliungen liber das Protoplasma, 1864, p. 101.- 



