April 15, 1921] 



SCIENCE 



371 



peratures of 49° C. in the sun in an unventi- 

 lated 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 centimeters of the one being measured, 

 but which had equivalent exposure.^ 



The elongation of the joints during this 

 youngest stage is directed by the temi)erature, 

 and the retardations due to maximum night 

 transpiration and acidity which come in later 

 are not yet manifest. The rate of elongation 

 therefore is greatest in midday and early 

 afternoon. Such a joint showing a tempera- 

 ture by the inserted thermometer of 43.5° C. 

 was subjected to the additional heating of the 

 electric grill at 1 :30 p.m. At 2 p.m. the tem- 

 perature passed 51° C. with growth still in 

 progress, the rate but little lessened from that 

 of 1 mm. in 24 hours which it was showing 

 at the beginning of the test. The tempera- 

 ture was now raised slowly until 3 p.m. the 

 joint stood at 51.5° C, the maximum at which 

 growth had ever been observed in any seed 

 plant. At 3:10 a temperature of 54.5° C. was 

 reached and five minutes later the readings 

 were 55.5° C. The joint was kept for an 

 hour between 55° and 55.5° C. during which 

 time the auxograph tracing showed a retarda- 

 tion but not a stoppage of growth. The heat 

 was shut off, the temperature soon falling to 

 42° C. and to 19° 0. at 9 p.m., when the 

 record assumed the character of that of the 

 preceding day of the same joint and of a 

 similar one standing near it. 



A repetition of the tests was made next day 

 at 10 A.M. when the joint stood at 33.5° C. 

 The heaters were brought into action, the 

 joint reaching 55° at 10:45 a.m. The prepa- 

 ration stood in the sun and was under normal 



1 MacDougal, D. T., and H. A. Spoehr, ' ' Growth 

 and Imbibition," Proc. Amer. Phil. Soc, 56, 289- 

 352, 1917. MoGee, J. M., ' ' The Effect of Position 

 upon the Temperature and Dry Weight of Joints 

 of Opuntia," Carnegie Inst. Wash. Year Book for 

 1916, p. 73. MaoDougal, D. T., "Hydration and 

 Growth," Carnegie Inst. Wash. Pub. 297, 1920. 

 DeVries, H., "MatSriaux p. 1. connaisance d. 

 1 'influence d. 1 temperature s. 1. plantes, " Arch. 

 Nierlandaises, III., p. 3, 1870. 



conditions of ventilation and transpiration. 

 Eeadings of 54.5° C. to 55.5° C. were made 

 for a period of an hour and a half during 

 which period the elongation was 0.2 mm. or 

 near the maximum rate for the species and 

 was still continuing. One heater was removed 

 at 12:15 midday and ten minutes later the 

 joint had fallen to 49.5° C. The cooling had 

 resulted in a minute reverse movement of the 

 auxograph recording lever of a character 

 which could only be attributed to the con- 

 traction of the metal and clay of the setting. 

 The temperature of the joints had fallen to 

 32° C. by 3 p.m. with no noticeable diminution 

 of the rate, the maximum being taken to lie 

 at some point over 40° C. 



A comparison of the thermometer with 

 U. S. Bureau, of Standards Ifo. Y618 gave an 

 error so small as to be negligible with regard 

 to the above data. Furthermore the young 

 joint continued its growth at a rate normal 

 to its developmental stage. 



These and previously published measure- 

 ments establish the following points: 



1. Growth in Opuntia may begin at 9° C. 

 and extend to 55° C. 



2. Young joints of Opuntia may endure 

 the maximum of 55° C. observed in mature 

 joints in midsummer, for periods of an hour 

 and a half, resuming elongation at lower 

 temperatures with no perceptible after-effects. 



3. A new high record for growth in Opuntia 

 and for the higher plants of 55° 0. <131° F.) 

 has been established by these experiru'ents. 



4. The maximum rate of growth of Opuntia 

 occurs between 37° C. and about 47°-49° C, 

 under which conditions a biocoUoid consist- 

 ing of 9 parts agar and 1 part protein under- 

 goes maximum swelling in water.^ 



5. 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 than, 

 albuminous substances. It is to be noted how- 

 ever that bacterial cells, which are highly 

 albuminous, may withstand high tempera- 



2MacDougal, D. T., "The Relation of Growth 

 and Swelling of Plants and BioooUoids to Tempera- 

 ture," Proc. Soc. Exper. Biol., 15, 48-50, 1917. 



