Imbibition and Growth of Opuntia. 



135 



tion or absorption action of the plasmatic colloids, which in the case 

 of Opuntia are probably low in proteins. 1 



The growth of etiolated shoots of Opuntia is of an indefinite char- 

 acter, as the length which such members may reach depends to 

 a large extent upon the amount of available material and other 

 features. Shoots which were already a few weeks old, and which had 

 developed in a dark chamber kept at 16 to 18 C. were found to be 

 growing at the rate of 5.2 mm. daily. These were removed to a 

 second chamber, hi which the temperature was kept steadily at 16 C. 

 for 3 days, during which time the rate varied from 3.1 mm. to 3.4 mm. 

 daily. The temperature was brought up to 21 to 23 C. in 3 hours, 

 and the rate was 5 mm. for the first day. During the second and 

 third days at this temperature the rate rose to 7 mm. per day. The 

 rate was 7.6 mm. daily during the next 2 days and about 8 mm. daily 

 for a final period of 16 hours. The temperature now being raised to 

 30 C. in 2 hours, and after that varying from 30 to 32.5 C., the rate 

 was 11 mm. daily during the first 16 hours, then at the rate of 16.8 mm. 

 during the succeeding 12 hours, during which time the elongation pro- 

 gressed in a remarkably uniform manner. 



I2p.m.2 4 6 8 10 m. 24 6 6 10p.m. 



FIG. 24. Auxographic record of varia- 

 tions of length of etiolated shoot of 

 Opuntia X26, at temperatures as be- 

 low, sheet ruled to 10 mm. intervals: (a) 

 downward movement of pen 7 h 30 m a. m. 

 to 9 h 40 m a. m. denoting growth at tem- 

 peratures of the stem of 45 to 49 C.; 

 (b) growth checked for 20 minutes at 

 49 C. ; (c) growth resumed at temper- 

 ature of 49 C. ; (d) shortening at 48.5 

 to 52 C. ; (e) stationary at 50.5 C.; 

 (/) growing at temperatures of 48 to 

 49 C.; (0) shortening at 49 C.; (h) 

 growing at 38 to 41 C. ; (t) shorten- 

 ing at 49 C. 



The rate itself was one which might have been identified with that 

 of a green plant, in which, however, the length of the cell-mass might 

 not be equivalent. The chief point of interest in the present con- 

 nection is that which comes from a comparison of the imbibition capac- 

 ity and growth. Sections grown at 17 to 19 C. showed an imbibi- 

 tion capacity at 30 to 31 C., nearly double that displayed at the lower 

 temperature, and it was also to be seen that shoots growing at the rate 



x Palladia, W. Transpiration als Ursache der Formanderung etiolirter Pflanzen. Ber d. deut. 

 bot.Ges., 8:364. 1890. 



