134 



Bulletin 79 



4. Opuntia sp. Burbank Special has a cooling point of — 1° C. 

 (30.2° F.) and a freezing point of —0.20° C. (31.64° F.),where it 

 remained from 22 to 30 minutes and dropped afterwards rapidly. 



5. 0. JusicauUs has a cooling point of — 1° C. (30.2° F.) and a 

 freezing point of — 0.50° C. (31.1° F.), where it remained from 45 

 to 64 minutes, and then dropped rapidly. 



6. O.ficus indica from Sicily reached its cooling point at — 0.75°C„ 

 (30.65° F.) and its freezing point at —0.50° C. (31.1° F.), where it 

 remained from 30 to 38 minutes and dropped afterwards until the 

 temperature of the test tube was reached, which was — 20° C. 

 (—4° F.). 



SUMMARY OF RESULTS OF TEN EXPERIMENTS WITH EACH OF SIX 

 SPECIES AND VARIETIES OF OPUNTIA 



Name of plant 



0. castillae 



0. ficus indica, Malta. 



O. Ellisiana 



Opuntia sp. Burbank 



Special 



O. fusicaidis 



O. ficus indica, Sicily. 



Cooling point 



-l.UO 

 -0.75 

 -0 . 75 



-1.00 

 -1.00 

 -0.75 



°F. 

 30.20 

 30.65 

 30.65 



30.20 

 30.20 

 30.65 



p'reezing point 



" c. 



-0 50 

 -0.25 

 -0.50 



-0 . 20 

 -0.50 

 -0.50 



" F. 

 31.10 

 31.55 

 31.10 



31.64 

 31.10 

 31.10 



Time of 

 freezing 



Mins. 

 35-44 

 12-18 

 20-28 



22-30 



45-64 

 30-38 



Temp, of the air 



°c. 



—20 

 —20 

 —20 



—20 

 —20 

 —20 



° F. 

 —4 

 —4 

 —4 



—4 

 —4 

 —4 



Results of other workers 



It is interesting to compare the above study with the results of 

 other experimenters with cacti and also with different plants. The 

 different species show a considerable range of temperature for the 

 freezing point and also for the duration of the freezing point. The 

 limited work that has been done on the species of cacti by other 

 investigators gives practically the same freezing point as found in 

 the writer's experiments. This would indicate that cacti have their 

 own biophysical peculiarities. 



Muller-Thurgau* in experiments with Phajus grandifoUus , a 

 tropical orchid, shows that the temperature of the plant in an 

 environment of —7.5° C. (18.5° F.) drops regularly from 15° C. 

 (59° F.) to— 2.5° C. (27.5° F.); after this it drops slowly until 

 —6° C.^21.2° F.) is reached. The temperature then rises to —0.5*' C. 



*Ueber das Gefrieren und Erfrieren dcr Pflanzfen, Landw. Jahrb. ISSO. 



