suggests tliat some cliaiigc took plac*' in ihc protoplasm 

 by aging. 



2. Algae. According to W. West and (J. S. AVest, 

 Spirogyra cataeniformis was in excellent vitality after 

 having been imbedded in ice for 2 weeks while in the 

 process of conjngation {Ann. of Bot., 12, 33, 1898). 



Cohn (1871) studied the vitality of Nitella syncarpa 

 cooled on a freezing stage on the microscope. Branches 

 of the alga were placed under a few mm. of water in a 

 shallow glass which was exposed to -20°. A thermome- 

 ter indicated the temperature of the water in the glass. 

 Active protoplasmic streaming could ])e observed at 0° 

 and slow movement could still be seen at -2°. After 

 exposure to lower temperatures, the cells were frozen and 

 killed, although, in 2 cases, cells taken from the ice at - 3° 

 were alive. Repeating these experiments with Nitella 

 branches not surrounded with water, Cohn observed the 

 protoplasmic streaming until the air temperature near the 

 alga registered - 2°. Ice formed in the cells between - 3° 

 and - 4° and the protoplasts shrunk. After thawing, the 

 cells were dead. 



Molisch (1897) froze tilaments of Spirogyra between 

 slide and coverslip at - 3° to - 6° and found, after thaw- 

 ing, disorganized chloroplasts and swollen nuclei charac- 

 teristic of dead cells. Death was observed also in Clado- 

 phora frozen at -8° in the same conditions, and in Der- 

 besia and Codium frozen at - 11°. 



Klemm (1895), using the method that we described 

 above under the heading ''Hair Cells," observed that 

 CJiara sprouts and Spirogyra filaments were killed after 

 an exposure of 15 minutes to - 13°, while protoplasmic 

 streaming could be resumed after exposures to higher 

 temperatures (-6°) or for shorter times and was only 

 slowed after a cooling to -2°. 



Kylin (1917) experimented on the effects of freezing 

 on sea algae. The material, immersed in sea water, Avas 

 cooled successively to the temperatures of -2.9°, -4.0°, 

 -5.7°, -7.8°, -10.7°, -16.8°, and -18° to -20° and the 



