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 takes place may be stated at C., although 2 has 

 been observed L in a single plant, Nitella syncarpa. 



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 2 observed that in the root-hairs of Hydro- 

 charis Morsus-ranae the 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 3 found that the 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 4 

 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. 

 They become more or less rounded, although very irregularly, 

 and may be completely disintegrated. Such changes have been 

 noted by Max Schultze 5 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 Kiihne, 6 such changes 

 take place within two minutes in the plasmodium of ^Ethalium 

 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, namely,, 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. 7 If, now, very gradual increments of heat 



1 Botan. Zeitung, 1871, p. 723 (Colin). 



2 Archiv. Neerlandaises, v., 1870, p. 385. 



3 Die Lehre von der Pflanzenzelle, 1867, p. 53. 



4 Flora, 1876, p. 213. 



6 Das Protoplasma d. Rhizopoden und Pflanzenzellen, 1863, p. 48. 



6 Untersuchungen liber das Protoplasma, 1864, p. 87. 



7 Untersuchungen iiber das Protoplasma, 1864, p. 101. 



