DEPARTMENT OF BOTANICAL RESEARCH. 47 



A New High-Temperature Record for Growth, by D. T. MacDougal and 



Earl B. Working. 



A record of growth of young joints of a prickly pear (Opuntia) at 

 50° C. and 51.5° C. and of the active elongation of etiolated stems of 

 the same plant growing at 49° C. was published in 1917 by MacDougal. 

 Dr. J. M. McGee had found previously that the mature joints of the 

 same Opuntia might reach temperatures of 55° C. in the open without 

 damage, which was a record for endurance of the higher plants in air 

 at the Desert Laboratory. In the repetition of the growth measure- 

 ments at the Desert Laboratory late in March and April 1921, young 

 joints which might reach temperatures of 49° C. in the sun in an 

 un ventilated glass house were heated further by the use of electric 

 grills. Temperatures were taken by mercurial thermometers with 

 bulbs of the clinical type thrust into joints within a few centi- 

 meters of the one being measured, but which had equivalent exposure. 

 These and previously published measurements establish the following 

 points : 



Growth in Opuntia may begin at 9° C. and extend to 58° C. 



Growth of young joints of Opuntia, the temperature of which rose to 

 62° C. (144° F.) in an air temperature of 63° C. (146°F.), stopped and 

 some shrinkage ensued, but growth or enlargement was resumed 

 when their temperature fell to 50° C. 



A new high record of 58° C. (137° F.) for growth in Opuntia and for 

 the higher plants has been established by these experiments. 



The maximum rate of growth of Opuntia occurs between 37° C. and 

 about 47° to 49° C, under which conditions a biocolloid consisting 

 of 9 parts agar and 1 part protein undergoes maximum swelling in 

 water. 



The cell colloids of Opuntia include a large proportion of pentosans 

 or mucilages, the colloidal condition of which is in general less affected 

 by the temperatures used tlian albuminous substances. It is to be 

 noted, however, that bacterial cells, which are highly albuminous, 

 may withstand high temperatures such as those of boiling water. 



The young joints which were subjected to these temperatures were 

 about 15 to 20 mm. in width and 25 mm. in length, and after being 

 held at or near the record temperatures for an hour or more, which was 

 repeated in one case, they carried forward normal development, 

 reaching maturity at a normal average of 100 mm. in width and 130 

 mm. in length. 



It is to be noted that data from observations in which temperatures 

 were taken from the air or from water in which the roots or aerial 

 parts of plants were immersed have but little value in any estimation 

 of the working temperature of active protoplasm by reason of the ab- 

 normal hydration and transpiration conditions introduced. These 



