No. 551] RELATIONS IN XENOPARASITE! 677 



Xenoparasitism of Cissus Laciniata 

 The induced parasite Cissus laciniata exhibits in the 

 structure and form of its roots (the shoot was not studied) 

 certain deviations from the normal which are of signifi- 

 cance and interest. A history of the experiments in which 

 this species was used as a parasite is given in another 

 place, suffice it to state here that a cutting of the Mexican 

 grape (Cissus laciniata) was introduced into the tissues of 

 Opuntia blakeana and allowed to remain several months. 

 A shoot with leaves and tendrils was formed. After the 

 culture had been running some time a root of the grape 

 was seen to emerge from the surface of the cactus, to 

 grow downwards, and to penetrate the soil. It was sev- 

 ered so that the Cissus had connections with the cactus 

 only. On June 10, 1912, the newly organized leaves were 

 ■seen to be relatively small and the tendrils not to develop. 

 The culture was thereupon taken down and the roots of 

 the parasite dissected out so that their relations to the 

 host tissue might be learned. 



All of the roots of Cissus which were situated within 

 the tissues of the cactus were found to be fleshy. A main 

 root was traced from the base of the cutting through the 

 tissues of the cactus for a distance of 3 cm. when, as 

 above mentioned, it issued from the cactus and found its 

 way into the soil. This root gave off one branch about 

 1 cm. from its point of origin, which extended for a dis- 

 tance of 3 cm. into the tissues of the cactus. The root last 

 mentioned gave rise in turn to a branch which attained a 

 length of 1.5 cm. In addition to these roots there were 

 several short ones which reached little belond the surface 

 of the parent root. All roots except the one especially 

 mentioned as not behaving in this manner were wholly 

 enclosed within tissues of the host. 



Structure or Free-livixg Roots 

 The portion of the roots which are free-living offer 

 useful points of comparison, for which purpose the anat- 

 omy will be briefly reviewed. 



