AUTONOMIC MOVEMENTS OF OPUNTIA. 37 



showed no growth. One of the etiolated opuntias, having - made no roots, 

 was reset. By the movement of the preparations one showed a geotropic 

 movement toward the perpendicular, one a heliotropic curvature toward a 

 window, while three displayed marked nutating movements, including one 

 in which this had originally been noted on May 17. The movement had 

 ceased during the high temperatures of the hot midsummer, but now was 

 again noticeable. (Further data concerning the movements are given in 

 a separate subsection below.) 



November 8, 1909. Two etiolated opuntias which had been established 

 in the body of an Echinocactus for 8 months or more were dissected after 

 having - shown some growth of the lateral and terminal expanding branches. 

 The walls of the cavity in the host had healed, forming a brownish layer 

 surrounding the base of the insertion closely and forming a connection by 

 which liquids might readily pass to the base of the inserted slip. No actual 

 union of the tissues had taken place, the base of the insertion being made 

 of clear pale-green tissue, with a thin epidermis, which might be capable 

 of giving rise to absorptive organs at any time. Several other preparations 

 were still alive. 



January JO, 1910. Several preparations of etiolated opuntias and green 

 stems of Opuntia versicolor were dissected. The submerged portions of the 

 stems were alive in most instances, but no roots had been formed. The 

 preceding period had been one of temperatures at which the plants used 

 as parasites display no growth activity. The clear, pale tissues of the sub- 

 merged portions of the stems had an aspect suggestive of a capacity for 

 carrying on the slow absorption which must have taken place. 



As may be seen by reference to data given in other sections of this paper, 

 the osmotic pressure of the sap of opuntias is higher than that of echino- 

 cacti under similar conditions. 



AUTONOMIC MOVEMENTS OF OPUNTIA. 



The etiolated branches used in the preparations consisted of flattened 

 stems 1.5 to 2.5 em. in width and 10 to 20 cm. in length. The secondary 

 branches, if they may be so termed, arose from terminal portions, and might 

 be either attenuated, thin, flattened in continuation of the structure of the 

 main branch, or in some instances the capacity for enlargement not having 

 been exhausted before the material was brought from the dark-room, small 

 oval joints were formed. The epidermal tissues of the stems w^ere more 

 or less brownish, especially near the base, but the power of growth seemed 

 to remain in the tissues throughout the entire length. 



On May 17, 1909, it was observed that an etiolated insertion which had 

 been set in the body of a bisnaga about a month previously, and which 

 had been recently brought into a shaded laboratory room, moved its tip 

 from a vertical position to one approximately horizontal, directing the apex 

 toward a window. The curvature was thought to be a heliotropic response, 

 but on the following day .it had moved its tip through 45 in retraction; 

 then a minor movement occurred, carrying the tip downward for two hours, 

 when the upward motion, carrying the tip toward the vertical, was resumed 

 and continued with a total departure of 3 cm. at 5 p. m. This phase of 



