DEPARTMENT OF BOTANICAL RESEARCH. 85 



with the result that the temperatui-e of the body fell as low as 4° C. 

 at 7 a. m. and reached a point at which growth ceased at about 8 p. m. 

 The steadily decreasing temperature was accompanied by a shrinkage — 

 due in all probability to lessened imbibition capacity as a result of low 

 temperature. Resumption of growth took place in the forenoon at 

 temperatures about identical with those of the previous year. The 

 total daily growth amounted to as much as 1.25 mm. to 1.5 mm. daily, 

 all of which was made between 9 a. m. and 8 p. m. 



The record of growth of Carnegiea included measurements of the 

 variations in the length of the spine as well as of coincident readings 

 of the swelling of the apical region of the stem near the base of the 

 spine. Elongation of the spine on daily rising temperatures began at 

 temperatures of 24° C, 18° C, 18° C, 15° C, 13° C, and 13° C. 

 on separate days and was very active at 32° C. A period of con- 

 tinuous elongation of the spine was comprised between April 10 and 

 17, 1916, during which time the air-temperature ranged between 

 14° C. and 28° C. The temperature of the body coincided with ^he 

 lower night temperature of the air and did not rise above 32° C. 



The maximum enlargement of the spine was at the rate of 0.075 

 nam. per hour, while that of the neighboring apical tract was not more 

 than a third of this rate. After the spine had reached nearly mature 

 length the apical tissue accelerated, showing a rate as 0.088 mm. per 

 hour. Growth began on rising temperatures of 15° C. and above and 

 was observed at 40° C. of the body. The main part of the growth took 

 place in the daytime and no action directly attributable to light effects 

 could be detected. 



Echinocadus and Carnegiea are active during the period in which the 

 temperature is within the tonic range, as taken from thermometers 

 inserted in the tissues. This implies that such plants grow during the 

 daylight period in the open and as far into the night as the temperature 

 permits, the maximum rate being attained during midday. Numerous 

 tests show but little variation in the acidity of Echinocadus and Car- 

 negiea and it is to be inferred that the cessation of growth and shrink- 

 age are purely temperature and transpiration effects, as the acidity 

 does not vary widely enough to modify the imbibition and growth 

 capacity of the cells as in Opuntia and other "som-" plants. 



Growth of Wheat {Triticum) and Corn (Zea), hy D. T. MacDougal. 



Most of the data concerning the rate and course of growth of these 

 two important crop-plants have been obtained chiefly by the measure- 

 ment of numbers of organs for a brief period. The facts of importance 

 in connection with the present paper have been obtained by analyses 

 of the march of growth from day to day. For example, the growth 

 of a single leaf was followed from March 19 to April 1, and the changes 

 in length of a leaf of corn from April 8 to April 22. 



