AGAVE-CARNHGIliA. 47 



lay in an open cavity with hardened walls. The roots did not come into 

 contact with the moist tissues of the host. In the second the cavity was 

 not so large, a dozen roots, many of them branching, had been formed, 

 and their apical portions were in contact with the clear greenish tissue of 

 the host, making possible some degree of parasitism. 



On July 30, 1909, the third preparation was in action when examined. 



AGAVE-CARNEGIEA. 



On January 21, 1909, a young Agave with leaves 30 to 40 cm. long was 

 trimmed both as to roots and leaves and the base set in a cavity in the 

 north side of a Carnegiea near the laboratory, being securely sealed by the 

 use of a large amount of plaster. The cavity had been originally formed 

 as a result of injury, had healed perfectly, and was lined with a heavy 

 corky tissue, which was cut away to leave the base of the stem of the 

 Agave in contact with the central cylinder of the stem. The preparation 

 remained intact and had shown no action when examined on July 30, 1909, 

 6 months later. 



Six other preparations were made in February, 1909, one being set in 

 the freshly-cut surface of a plant which had been decapitated. This prep- 

 aration was shaded and appeared to have made some growth when exam- 

 ined on July 30, 1909. Two of the other preparations were not in very 

 good condition, and two were apparently normal as to the condition of the 

 parasite. 



On October 11, 1909, the Agave set in the stump of a sahuaro near the 

 laboratory had made a growth of several centimeters in length of the leaves 

 and was apparently normal. The larger plant, set deep in the cavity in 

 the northern side of another sahuaro, had elongated the inner leaves to a 

 length of several centimeters, and also showed a swollen base indicative of 

 accession of water and food-material. None of the other preparations were 

 in very good order, although still surviving. 



On November 9, 1909, the Agave set in top of stump of sahuaro was 

 dissected. Roots had been formed which ramified between the corky layer 

 and the plaster, but no penetration had been made. The slip was dried 

 and shrunken as if it had received nothing from the host. 



On February 3, 1910, all of the preparations had been dissected except 

 the one in which an Agave was set in the side of a tall sahuaro. The apices 

 of the leaves had been slightly affected by the freezing temperatures, but 

 the bases remained plump and healthy. No growth is made by this plant 

 except during the period of higher temperatures. 



The high osmotic activity of the sap of Agave acts to prevent its desic- 

 cation under very arid conditions, and undoubtedly the inclosure of the 

 swollen base of the plant in a cavity with plaster facilitates the withdrawal 

 of some liquid from the tissues of the sahuaro, although separated by very 

 refractory or dense coatings. 



