The Temperature Relation 



413 



Soak some seed of barley or peas an hour or two in water 

 and keep another lot dry. Expose lots of 25, soaked and un- 

 soaked, to such low temperatures as may be conveniently 

 prepared by freezing mixtures of salt and ice. One lot may be 

 placed in test-tubes immersed in broken ice, another in similar 

 tubes at from 5 to 10 below zero, and another exposed to about 

 20 C. ; from 5 to 10 C. may be obtained in a freez- 



FIG. 112. Thermograph. [Illustration from Julien P. Friez.] 



ing mixture of 10 parts common salt to 100 parts snow, while 

 20 C. requires 33 parts salt. Subsequently, test the ger- 

 mination and discuss the results. 



Formation of ice crystals. Place filaments of Spirogyra in a 

 drop of olive oil in a hanging-drop culture. Expose in a cham- 

 ber surrounded by a freezing mixture such that the tempera- 

 ture of the chamber is reduced to about 10 C., then remove 

 the culture and examine promptly under the microscope to 

 locate position of any ice crystals formed. 



On a day when the temperature of the air is about C., 

 or below, make sections of artificially or naturally frozen buds 

 and locate the ice crystals. 



Effects upon root elongation. By means of the method em- 

 ployed in the study of growth, mark with parallel lines on the 



