36 THE EXPERIMENTAL INDUCTION OF DEPENDENT NUTRITION. 



CISSUS-FOUQUIERIA. 



The soft stems of Fouquieria have a soft cortex in which the accumulated 

 water-balance varies greatly, but is always large when a plentiful supply 

 is present in the substratum. Only a few combinations of Cissus with this 

 plant were tried. A portion of the tissue of the host would be cut away 

 and a slip held in place against the cortex by plaster. Preparations of 

 this kind were made in March, 1908, which showed no development except 

 the formation of aerial roots, and perished a month or two later. A second 

 lot was prepared in November, 1908, but all of these had died by April, 

 1909, without showing any action. 



OPUNTIA-ECHINOCACTUS. 



The combination made under this head include several species of flat- 

 tened and cylindrical opuntias, and in all cases constituted a union between 

 two forms with a large, fluctuating water-balance. A few freshly-cut slips 

 of Opuntia leptocaulis were used for insertion in the body of a plant in the 

 open air in February, 1908, but being fully exposed to the air and sun were 

 all killed by midsummer of the same year. 



January 21, 1909. - A regenerated plant consisting of a joint and a half, 

 the latter healed and regenerated, was set in a longitudinal incision in a 

 furrow of Echinocactus and sealed with plaster. A flower-bud was formed 

 and opened in April, but the fruit was aborted. The inserted slip main- 

 tained its turgidity throughout the summer. A crate affording - some 

 shelter was set over the host, primarily to avoid injury from animals. 



January 27 ', 1909. A young plant of Opuntia versicolor was taken up, 

 its root-system trimmed, and the remaining main root set in the body of 

 an Echinocactus in the glass-house- A few days later a similar preparation 

 of O. mamillaia was made, but this did not survive the arid foresummer. 



Aprils, 1909. A number of etiolated branches of Opuntia had been 

 regenerated in the sand-bed and after a few roots had been formed these 

 were trimmed- closely and set with the bases of the stems in cavities in the 

 bodies of echinocacti. On this date one of these preparations showed two 

 active buds; one only had perished. (See plate 7.) 



May 7, 1909. Three more of such etiolated greened shoots on Echino- 

 cactus were developing new buds; only one remained wholly quiescent. 



May 17, 1909. An etiolated shoot showed nutatory movements. 



May 20, 1909. Five etiolated greened slips of Opuntia were inserted in 

 a large Echinocactus in the open which was shaded by a wooden crate. 



June 3, 1909. Three of the last-named preparations were alive. 



June 30, 1909. All of the etiolated shoots on the Echinocachis in the open 

 were dead. Those in the laboratory rooms were alive, but had made 

 almost no growth within a month, while the one formerly displaying such 

 a marked nutatory movement was now as nearly stationary as such plants 

 usually are. 



October 2, 1909. Eight etoliated greened slips of Opuntia blakeana on 

 three bisnaga hosts were alive on this day. All were brought together in a 

 shaded laboratory room, together with two insertions of Opuntia versicolor 

 (young plants) and two detached branches. The latter were turgid, but 



