40 



yen, (lirrctly in coiitacl with llu' lluid. X()lliiii<4' abnonnal 

 was observed in liicir g'ermination. In anotlier experi- 

 ment, spores of 2 of the above genera, previously desic- 

 cated and maintained in a vacuum of 10 " mm. of mercury, 

 were immersed in li(|uid lielium at 4° K. for i) liours and 

 at 1.84° K. for 1 hour. No injurious effects resulted 

 (Becquerel, li);J2a). 



The spores of the feni, Polystichuni filix mas, previously 

 desiccated, sealed in the highest obtainable vacuum and 

 maintained for () hours in liquid helium between 5° and 3° 

 K. and for f) hours at 3° K., germinated like the controls 

 (Becquerel, 1930). 



Pollen gvsans of AiifirrJiiinou and Nicofiaiia, thoroughly 

 dried, in sealed tubes, in a vacuum of 10 ' mm. of mercury, 

 were put in liquid helium for 7 hours, the lowest tempera- 

 ture reached being 1.3° K. ; this did not weaken the ger- 

 minating power of the grains (Becquerel, 1929). 



4. Seeds. Seeds have been a subject of predilection for 

 investigators of the effects of low temperatures. 



Edwards and Colin (1834) subjected seeds of barley, 

 oafs and wheat for 15 minutes to - 40° (by the evaporation 

 of sulphur dioxide in the vacuum) and noticed no impair- 

 ment in their germinating power. 



Wartman (1860 and 1884) exposed 9 species of seeds, 

 from 20 minutes to 2 hours, to temperatures from - 78° 

 to -110° (ether and car])on dioxide) and observed no in- 

 jurious effect in them. The seeds were enclosed in sealed 

 tubes. 



De Candolle and Pictet (1879) subjected various seeds 

 to temperatures between - 40° and - 50° for about 4 hours, 

 and in another experiment, to -80° for more than one 

 hour; in no case did they observe any action of the cold 

 on germination. In a later experiment (1884), the same 

 authors subjected seeds of 8 species, dried in the air and 

 enclosed in sealed tubes, to a temperature lower than 

 -100° (by evaporation of carbon dioxide) and they ex- 

 tended the time to 4 days. This prolonged action of low 

 temperature had no effect on the seeds. 



