Distribution of the Giant Cactus. 143 



freezing, alongside unfrozen controls of the same size which had 

 been gathered at the same time and treated in every other respect 

 in the same manner. Within two weeks after freezing all three 

 cacti had begun to show a blackening of their tissues around the 

 base, which through a disturbance of their turgidity lost them 

 their natural erect position. By four weeks after the freezing 

 No. 12 had become black and soft throughout its lower half. 

 Six weeks aftei the f eezing No. 1 and No. 5 were photographed 

 (Fig. 2) so as to show the injured tissues at the base. These 

 individuals were kept for another month and failed to heal or 

 show signs of recovery, at the same time that the controls were 

 still in normal condition. 



Seven other young cacti were subjected to freezing tempera- 

 tures for periods as follows: 



No. 4 9 hrs. No. 19 (jjrecoi led 4 hrs.) . . 6 hrs. 



No. 9 6 hrs. No. 24 14 hrs. 



No. 13 15 hrs. No. 25 14 hrs. 



No. 18 (precooled 2 hrs.) . . 6 hrs. 



None of these individuals showed signs of injury from frost 

 on being kept for two months in the greenhouse with the others. 

 Two of tlicm. No. 18 and No. 13, are shown in Fig. 3. 



Seven seedlings of Giant Cactus one }ear old were sub- 

 jected to periods of freezing of from 6 to 42 hours. None of 

 the three subjected to 42 hours survived, but one subjected to 

 9 hours, and one to 15 hours perished. The fact that the seed- 

 lings were hot-house grown, more succulent and less heavily 

 cuticularised than outdoor seedlings probably are * prevents 

 me from drawing any conclusions as to their being less resistant 

 than the juveniles and adults. 



Although the conditions under which these experiments 

 were done were somewhat artificial as respects the coldness of 

 the soil and the high humidity of the air surrounding the plants 

 at the time of exposure to cold, yet I cannot believe that these 

 conditions affect the results materially. The seven experi- 

 ments in which individuals were subjected to periods of from 

 6 to 15 hours of frost reduplicated conditions under which the 

 Giant Cactus is placed in nature, and their survival was no 

 more than a confirmation of what might be observed in the 



•I have never seen any spontaneous seedlings of this size in the field, nor has anyone else, 

 so far as I know. 



