MACDOUGAL: MECHANISM AND CONDITIONS OF GROWTH II 



It is believed that no such previous relation between the actual 

 growth phenomena and internal conditions had ever before been 

 achieved in studies on this general subject. 



In addition to such determinations of the physical conditions 

 of the disks, the results of some measurements begun in 191 1 upon 

 the general alterations in form and size of the joints were also 

 available. These show that while the main growth is accom- 

 plished during the initial season of enlargement, yet some distinct 

 variations in size ensue during the second season. The dimensions 

 of some joints of Opimtia discata at Tucson in the warm arid 

 climate of the Desert Laboratory and at Carmel in a cool equable 

 climate are given below: 



Measurement of joints of Opuntia discata: 



No. I. {Tucson) 

 Date Width Length 



May 9, 1912 6.5 cm. 7.0 cm. 



May 18, 1912 II. 5 12.3 



May 29, 1912 13.4 14.6 



June 9, 1912 14.0 15.0 



Sept. 24, 1912 19.8 20.2 



March 9, 1913 19.6 20.2 



May 9, 1913 19.8 19.6 



June 18, 1913 20.0 19.8 



April 3, 1914 20.0 20.0 



No. 2. {Tucson) 



May 9, 1912 10.8 12.0 



May 18,1912 14.I 15. 1 



May 29,1912 15. 1 17.2 



June 9. 1912 15.4 17.2 



Sept. 24, 1912 18.5 20.0 



March 9, 1913 18.5 20.6 



May 9, 1913 18.4 20.8 



June 18, 1913 18.2 20.0 



April 3,1914 21.2 18.0 



No. 3. {Tucson) 



May 9, 1912 6.0 7.0 



May 18, 1912 9.8 II. o 



May 29, 1912 1 1.2 13.2 



June 9,1912 II. 8 13.2 



Sept. 24, 1912 15.2 16.8 



March 9, 1913 15.3 17.2 



May 9, 1913 15.2 17.0 



June 18,1913 15.3 17.0 



April 3, 1914 16.2 17.2 



