94 RELATION OF PLANTS TO TEMPERATURE 



of an eye-piece micrometer. Connect the inlet and outlet pipes 

 properly and arrange a vessel to be heated by a gas flame or 

 alcohol lamp for furnishing warm water. This should be placed 

 above the level of the stage and should be controlled by a pinch- 

 cock which will regulate the amount of water flowing through the 

 warm stage. Raise the temperature of the slide to 37 C. Com- 

 pare rapidity of movement with that of previous temperature. 

 Open the stopcock and allow a rapid flow of warm water, rais- 

 ing the temperature to 42 C. Note results. Raise the tem- 

 perature by accessions of 5 C. until movement ceases. De- 

 termine the point of heat rigor, from which the cell may recover 

 and resume motion. Determine the point of death rigor and note 

 behavior of protoplasm. The slip lying on the warm stage will 

 be one or two degrees colder than the reading of the thermom- 

 eter provided for the stage. This error must be calibrated and 

 taken into account in all readings. 1 



Mount a fresh object and place melting ice in the supply vessel 

 taking away the lamp. Lower the temperature to 25 C., 20 C. 

 18 C., 16 C., andlowerby intervals of 2 noting minimum and 

 fatal temperature producing cold rigor and death. Expose fresh 

 material suddenly to each of the above temperatures to deter- 

 mine whether acclimatization has taken place in the previous tests. 



146. Relation of Low Temperatures to Resting Period of Bulbs 

 and Tubers. Secure two dozen hardy bulbs or tubers of potato 

 or Arisaema, or some hardy plant. Bury half of the lot in the 

 soil out-of-doors and allow them to remain where they will re- 

 ceive the prevalent out-of-door temperatures until December I st. 

 Imbed the remainder in sawdust and set in dark corner of green- 

 house or laboratory where the temperature does not fall to 40 

 C. The first lot may be placed in a refrigerator in which pro- 

 visions are kept instead of being buried in the soil from Septem- 

 ber to December. Now place both lots in pots using proper 

 methods of culture and set in temperate room with temperature 

 between 60 and 65 F. Note the behavior of the two lots. 



1 Beal, W. J. Bromus secalinus germinating on ice. Bot. Gazette, 23 : 204. 1897. 



