OPUNTIA-CAK\K(;iKA. 43 



August, 1908. — Several insertions of Opuntia leptocaulis and O. versi- 

 color were set in a trunk of Carnegiea and sealed with plaster. 



October 30, 1908. — Three additional healed cutting* of Opuntia versicolor 

 were inserted in the trunk of Carnegiea. The O. blaktaua on stump erf a 

 host plant had become firmly embedded. 



January 23, 1909. — A young plantlet of Opuntia versicolor, in its first 

 year, was taken from the soil, the roots trimmed back, the whole basal 

 part of the plant being - inserted in a cavity of a Carnegiea near the glass- 

 house. This cavity was made by cutting- out the black incrustation from 

 the surface of a former wound. The preparation was sealed with a liberal 

 supply of plaster. 



March 30, 1909. — One insertion of Opuntia versicolor on host first used 

 was showing an active bud. 



April 5, 1909.— An etiolated greened stem of Opuntia was sealed into 

 the freshly-cut upper surface of a Carnegiea, in which similar cuttings of 

 Cissus, Agave, and others were put at the same time. 



June 12, 1909. — The Opuntia blakeana on stump of host had not made any 

 growth. An insertion of the same plant on the surface of a trunk nearby 

 had made no growth. The 0. versicolor plantlet on tall host had made no 

 growth and was of a yellowish color. Several of the insertions, including 

 more than one species, were in a dying condition, but the etiolated greened 

 0. blakeana on stump with other insertions was alive and growing. 



July 30, 1909. — The supply of moisture had not changed the condition 

 of the arrangements on this date, with the exception of those made with 

 Opuntia versicolor. All insertions of this plant were plump and turgid and 

 were showing a fair amount of growth. 



October 2, 1909. — A review of all the preparations showed that all the 

 etiolated shoots of Opuntia inserted in Carnegiea were dead. Two plants 

 of Opuntia blakeana on Carnegiea had survived the summer and were tur- 

 gid, but had made no growth in size or by addition of joints. The plantlet of 

 Opuntia versicolor on tall host-plant near glass-house was apparently in a 

 healthy condition, although slightly yellowish in color, in agreement with 

 the condition of hundreds of normal specimens growing in the soil. Seven 

 insertions in the basal part of another host were alive. Three of these 

 were dead in the basal portion and were deriving but little from the host. 

 The remainder seemed to have contact of living tissue with host. 



November 9, 1909.— A dissection of the arrangement of Opuntia blake- 

 ana on sahuaro showed that the base of the stem incased in plaster had 

 given rise to a number of roots, which were closely pressed against the 

 thin, hard, indurated corky layer which is formed by the sahuaro when 

 the air is excluded partially. No actual penetration had occurred, although 

 the Opuntia had not desiccated as if lying free, suggesting that some 

 material had been received from the host. 



January 8, 1910. — Several preparations of Opuntia versicolor on Carnegiea 

 were still alive, but with the xeno-parasite showing the effects of an inade- 

 quate supply of water. Three were especially plump and turgid. 



On January 10, 1910, all of the arrangements of Opuntia versicolor upon 

 Carnegiea except three were dissected. The host had in all instances formed 

 a corky layer on the surfaces exposed to contact with the xeno-parasite. 

 Despite this fact the insertions of Opuntia had withdrawn sufficient liquid 

 to preserve a fairly plump condition, though not so turgid as branches of 



