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- 



OBSERVATORY, BALTIMORE. MD, 



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 



