Cold-Resistance; in Spineless Cacti 



135 



<^31.1° F.), where it remains for about 4 minutes, after which it drops 

 regularly and gradually to — ^6.75'^ C. (19.85° F.) in 41 minutes. 



In his experiment with potatoes, MuUer-Thurgau found that 

 the temperature dropped regularly from 15° C. (59° F.) to 2° C. 

 (35.6° F.) From the latter to —3.3° C. (26° F.) it dropped 

 more slowly ; after that the temperature rose rapidly to 2° C. 

 (35.6° F.) and remained there for 70 minutes. With this the air 

 in the experiment was changed to 15° C. (59° F.) so the freezing 

 experiment could be carried no further. 



MuUer-Thurgau gives a long list of freezing points of different 

 plants, from which several well-known species have been selected for 

 comparison with the freezing points of cacti. 



TABLE OF FREEZING POINTS OF DIFFERENT PLANTS. 



Comparison of results 



The results of the writer's work with cacti closely resemble 

 those which MuUer-Thurgau obtained with Opuntia maxima. He 

 obtained a relatively high cooling point, and a freezing point 

 a little below the temperature at which water freezes, while 

 with other plants he obtained both a lower cooling point and a 



