42 THE EXPERIMENTAL INDUCTION OF DEPENDENT NUTRITION. 



adaptive variation, and the supposition arises that perhaps many unusual 

 activities displayed by organisms under highly specialized conditions are 

 equally non-adaptive, although resulting directly or indirectly from the 

 action of environic factors. 



OPUNTIA-OPUNTIA. 



On February 12 an etiolated shoot of Opuntia which had been cut and 

 allowed to regenerate and green in the sand-bed was inserted in a cavity 

 made for it in a rooted joint of Opuntia discata. This seeming to be in 

 good order, the whole preparation was put in the dark-room on March 2, 

 1909. Slips of O. leptocaulis had been inserted in joints of O. discata early 

 in 1908 and these lived and developed new branches indicative of grafting. 



OPUNTIA-FOUQUIERIA. 



A number of slips or single joints which had formed calluses at the base 

 were fastened to stems of Fouquieria in places where the epidermal tissues 

 had been removed early in 1909. It was difficult to bring about good 

 contact between the parasite and host, so that most of the preparations 

 were unsuccessful, although plaster was used to seal and hold the parts 

 in position. On July 30, 1909, one such preparation was alive and turgid, 

 although no growth had been made. On October 8, 1909, this prepara- 

 tion was taken down and it was found that the joint of Opuntia was dead 

 at the base, having no capacity to absorb from the tissues of the host, 

 which were completely callused. 



OPIINTIA-CARNEGIEA. 



The series of preparations of these two plants were begun by the use of 

 freshly-citt slips of Opuntia which were inserted in cavities made in the 

 trunks of Carnegiea distances of 1 to 2 meters from the base and sealed 

 with gelatin. The host exudes a quantity of sap, which quickly turns 

 brown and blackish, and the seals were soon destroyed. Later plaster was 

 substituted for the gelatin, and also the practice was followed of making 

 the cavity of such size that the insertion of the slip would close it com- 

 pletely, a thing easily done by reason of the great turgescence of the tissues 

 of the enforced host. The first preparations were made on January 30, 1908. 



March ■/, 1908. — The exposed surfaces of the hosts were covered with 

 a hard black coat in which the roots and basal portions of the inserted 

 slips were incased. Of course some moisture might pass through this 

 layer, and the xeno-parasites were all plump and turgid, and were in the 

 same condition as late as May 22, 1908. A number of cylindrical and 

 flat opuntias had been used in the arrangements. A regenerated plant 

 consisting of a basal fragmentary joint of Opuntia blakeana, with roots 

 issuing from the lower surface, was seated snugly on the concave surface 

 of a living stump of Carnegiea which was fully healed and covered with 

 corky plates. The loose plates were pried away. A few weeks later the 

 Opuntia was fixed in place by means of plaster. 



