226 THE BIOLOGY OF FLOWERING PLANTS 



developed into vigorous plants the apple foliage was entirely 

 pruned off. For a year the mistletoe throve, and then the 

 apple stocks died off and with them the mistletoe. The 

 parasite supplies nothing to its host, and can draw supplies 

 from it only when it is living. 



In other members of the family methods of attachment 

 very different from that described are to be found. In 

 Loranthus eiiropcem, the golden-green mistletoe which 

 grows on evergreen oaks in the Mediterranean countries, 

 the branches which arise from the primary sucker grow, not 

 in the cortex, but in the cambium and into the wood of the 

 host, thus making direct connection. When the resistance 

 of the older wood becomes too great to allow of further 

 penetration the tips turn outwards, and the repetition of 

 the process gives rise to a curious step-like appearance of 

 the absorbing organs of the parasite in longitudinal section. 

 These branches keep pace for a time with the growth in 

 thickness of the host wood, but may ultimately become more 

 or less completely embedded. In some American genera, 

 e.g. Phoradendron, the mistletoe of the United States, and 

 also in some species of Loranthus, after the penetration 

 of the primary sucker the tissues of the adhesive disc grow 

 out marginally ; stimulated by the contact of the parasite 

 the host tissues grow out also, forming a disc or cup of some 

 size. In the most extreme cases the wood of the host 

 forms a convoluted, lobed cup over 6 in. in diameter, 

 completely surrounding the disc of the parasite. These 

 remarkable objects are known in Mexico as Rosa de Palo 



In the majority of tropical species true adventitious roots 

 are produced either from the stem above the original adhesive 

 disc or, in species with long twining stems, at any point on 

 these. The behaviour of these adventitious roots is very 

 varied. In some species they grow irregularly, forming an 

 interlacing network with each other and with host branches ; 

 in others they grow along the host branches ; in yet others 

 they behave like tendrils twining securely round any solid 

 object. In all cases they give rise to adhesive discs from 



