67 



time necessary to kill the algae at any of these tempera- 

 tures noted. As a sign of death, he used the changing 

 color exhibited by the brown and the red algae and the 

 loss of the plasmolysing power for the green algae. He 

 found that these plants were never killed by low tempera- 

 ture in the subcooled condition, the pigment not being re- 

 leased when ice was not formed. The death tempera- 

 tures and the corresponding lethal times of exposure were 

 as follows: TraiUiella, -2.8°, 3 hours; Delesseria and 

 Laurencia, -4°, 10 hours; Laminaria (1 year old) -5.7°, 

 6 hours; Cerammm, -5.7°, 10 hours; Laminaria (several 

 years old) -16.8°, 3 hours; Chondrus, -16.8°, 10 hours; 

 CladopJiora, - 18° to - 20°, 3 hours ; PylaieUa, - 10° to - 20°, 

 10 hours; other species such as Nemalion, PorpJiyra, 

 Fucus, Enteromorpha were alive after 10 hours at - 18° 

 to -20°. Kylin obtained thus a surprisingly large differ- 

 ence in the death temperatures of the various kinds of 

 algae. 



According to Karcher (1931), Pediastrum and Hor- 

 midium cultivated on agar slants in glass tubes, and im- 

 mersed for 5 hours in a freezing mixture at - 70°, were not 

 killed. 



Becquerel (1936) investigated the vitality of dried 

 algae subjected to the temperatures of liquid gases. He 

 took samples of soils containing various algae and gradu- 

 ally dried them in a vacuum with barium oxide, at 35°, 

 for 3 months. He then placed a portion of the soils in 

 glass tubes closed with cotton plugs and sealed another 

 portion in tubes evacuated to 10' mm. of mercury. 

 Thereupon he subjected all of them to liquid helium 

 (- 269° to - 271°) for 71 hours, and to liquid nitrogen for 

 480 hours. Both groups of soils yielded living Oscilla- 

 toria, Glaeotila, Hormidium, Siphonema and Pediastrum. 



According to the same author (1932b), the filamentous 

 alga Tribonema elegans, thoroughly dried on a piece of 

 bark, kept in a high vacuum for 22 years and exposed for 

 several hours to temperatures from 4° to 1.84° K., grew 

 after that treatment. 



