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.^ 



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 amoxmt 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, in 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 nun. 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 hom-s. The temperature now being raised to 

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

 was 11 mm. daUy 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 imiform manner. 



I2p.m.2 468 10 m. 2460 lOpm. 



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''30™ a. m. 

 to 9''40" a. m. denoting growth at tem- 

 peratures of the stem of 45° to 49° C. ; 

 (6) growth checked for 20 minutes at 

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

 ature of 49° C; (d) shortening at 48.6° 

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

 (/) growing at temperatures of 48° to 

 49° C; (ff) shortening at 49° C; (h) 

 growing at 38° to 41° C. ; (i) 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 



^Falladin, W. Transpiration als UrsachederFormanderungetiolirter Pflanzen. Ber d. deut. 

 bot. Ges., 8: 364. 1890. 



