MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 299 



39° C. at I P.M. March 29; at 35° C. at 1:30 P.M. April 4; at 

 32° C. at 3 P.M. April 5; at 36° C. at 1:30 P.M April 6; 37° C. 

 at 2 P.M. April 7. The upper temperature limit is given in other 

 records included in the present paper, the extreme highest recorded 

 being 51.5° C. 



A second series of cultures for observation of growth and 

 temperature were arranged at the Coastal Laboratory, Carmel, Cali- 

 fornia, in the summer of 191 6. Preparations consisting of an old 

 joint with roots were placed in a dark chamber in which tempera- 

 ture could be controlled. The basal joints from which the buds 

 arose held a supply of reserve material quite adequate for the de- 

 velopment of the etiolated shoots. Some of the latter were grow- 

 ing vigorously six months after the close of the tests described. 



These tests were made under conditions different from those en- 

 countered by the plants in the open in two important essentials, viz. : 

 the temperature did not rise to a daily maximum and fall to a 

 nightly minimum, but was maintained at fixed levels or varied as 

 described and the action of light was excluded except for brief 

 intervals when observations were being made. The effect of such 

 conditions would be to exclude the disintegrating action of light on 

 the acids resulting from respiration, and also to make photosynthesis 

 impossible. Both of these features contribute to the daily variation 

 in growth of plants in the open. Growth of shoots in darkness 

 may be taken to be normal otherwise, so far as respiration and im- 

 bibition are concerned. 



An etiolated shoot of Opuntia discata which had arisen in the 

 dark chamber in which it had been placed in May, 1916, having a 

 length of 65 mm. and a width of 15 mm., was chosen for the first 

 test, which was duplicated by later ones. The container in which 

 the plant stood was fastened firmly in place and an auxograph was 

 brought into contact with it adjusted to record alterations in length 

 magnified twenty times. A small thermometer with thin bulb of 

 the "clinical " type was inserted in the old joint near the base of the 

 young shoot and its readings taken to be those of the growing organ. 

 The difiference between the two could be only very slight. The 

 amount of growth displayed by the shoot on five successive days 

 was 1.2, I, .1, I and i.i mm. at temperatures of i7°-i8° C, July 



