594 SCIENCE PROGRESS. 



in vacuo ; the exposure lasted more than twenty minutes, 

 and the temperature sank to — i lo'C. Every seed germi- 

 nated. It might be reasonably urged that exposure was 

 here also inadequate for the acquisition of this low tempera- 

 ture by the seeds. A further communication appeared later 

 (12); seeds of Aiesctihis Hippocastcuiiini were wrapped in 

 the tin-foil and placed in a paste like that mentioned above, 

 in vacuo ; exposure lasted two hours and the temperature 

 was at least — i io°C. Germination occurred as in controls. 

 This experiment yields doubtful results ; the seeds may, or 

 may not, have acquired the temperature in question through- 

 out. De Candolle and Pictet {13) utilised liquid sulphur- 

 dioxide and nitrogen-monoxide as refrigerating agents. 

 In their first experiment four tubes of thin glass, each en- 

 closing seeds of the same species with metallic fragments, 

 were hermetically sealed and placed in a test-tube, that was 

 also hermetically sealed. The latter was covered with tow, 

 which was constantly sprinkled with sulphur-dioxide, and 

 exposed to air. The tube was thus submitted to gradual 

 lowering of temperature from — 39°C. to — 50'C. for six 

 consecutive hours. All seeds of three species germinated 

 as in the controls. Of twenty-four seeds of Tritic7im 

 {vulgare ?\ only seven germinated, but the authors attribute 

 this to an accident. In their second experiment thirty 

 species w^ere tested. When — 40'C. had been reached, 

 nitrogen-monoxide was poured several times into the tube 

 with the seed-tubes. At the close of the experiment that 

 lasted two hours the temperature was — 8o°C., which was 

 supposed to have obtained for at least an hour. No pre- 

 cautions were taken to graduate thawing, and the seeds 

 were not previously desiccated. Every lot, among w^hich 

 was Tritiaun, germinated except three, in which cases the 

 controls also refused to germinate. The first experiment 

 is probably reliable ; the second is dubious on account of 

 shortness of exposure. In a subsequent paper (14) seeds 

 of several species were kept for four consecutive days at a 

 temperature lower than — ioo°C., obtained through evapora- 

 tion of solid carbon-dioxide. Germination was normal in 

 four lots ; in four others it did not occur, as also in the 



