DEPARTMENT OF BOTANICAL RESEARCH. 57 



returns to 16° to 18° C. would be responsible for a rate higher than the 

 preceding one at that temperature. The average rate at 16° to 18° C. 

 was first found to be 1.5 mm. daily and that at 26° C. was 3.1 mm. 

 daily, giving a coefficient of 2 for the rise of 10° C. Inspection of 

 other results gave higher values. A point is reached below 35° C. 

 where a maximum rate is obtained which is not maintained. When a 

 plant is placed under constant exposure to any temperature in their 

 range, a decreasing high rate is exhibited. When this has run its 

 course, a new rise in temperature is followed by a new maximum, from 

 which the plant slows down. This stepping up and sliding back 

 appears to prevail practically to the upper hmit of growth. 



The observations reach the high hmit of 49° C. for the growth of 

 the higher plants. A new limit of endurance of 52° C. for growing plants 

 was also observed. Growth after such exposure was resumed at the 

 high hmit of 49° C. as before. 



The discovery of these upper limits of endurance and growth of 

 developing organs are probably conditioned on the use of new methods 

 of taking temperature rather than upon any specialization of the 

 protoplasm of the cacti. It has been assumed that the temperature 

 of growing organs approximated that of the air in nearly all studies 

 which have hitherto been made on this subject. A. M. Smith secured 

 body temperatures of the giant bamboo {Dendrocalamus giganteus) as 

 much as 6° C. above that of the air in his work on the growth of that 

 plant in Ceylon in 1906, and the use of such temperatures made 

 possible some advanced generalizations. The differences between the 

 temperature of the air and of the growing shoots of cacti are as much 

 as 8° or 9° C. at times. Thermometers of the '' chnical" type with thin 

 bulbs were used. The thin bulbs were fixed in the tissues of joints 

 from which new shoots were arising, and in growing shoots similar 

 to those being measured. 



A Precision Auxograph, by D. T. MacDougal. 



The changes in volume of growing organs and the measurement of 

 the swelhng of colloids similar to those concerned in the process have 

 made necessary the designing of recording apparatus applicable to 

 both kinds of material. The essential part of such an apparatus con- 

 sists of a dehcately balanced compound lever, carrying a tracing-pen 

 on one free end and having an arrangement by which the movement to 

 be measured may be applied at various intervals on the other free arm. 

 Magnifications of 10 to 50 are secured in this manner. A clock-driven 

 cylinder of the standard used in thermographs, barographs, etc., 

 carries the recording sheet, which has been specially designed. The 

 ruled space on these sheets is 8 cm., divided into milHmeters, numbered 

 on the ''fives" and shaded on the ''tens." The paper is of a quaUty 



