208 The Plant World. 



Singularly enough, the modifications exhibited by parasites 

 are not due directly or alone to the food received from the host 

 or symbiont, a similar effects are not seen when plants 

 are fed with solutions of organic materials which might be ob- 

 tained by parasitism. The entire set of complicated conditions 

 furnished by active association with a living host or co-operating 

 organism seems to be necessary to induce the changes described. 



The studies of the general anatomical features presented 

 by the families, the members of which exhibit parasitism, have 

 so far failed to yield any conclusions as to the morphological 

 features which might be favorable to such arrangements. The 

 specialization of tissue which ensues when a seed-plant becomes 

 parasitic fortuitously is far more striking than any simple 

 anatomical character which might be interpreted to indicate a 

 predisposition to the dependent habit of nutrition in autophytes. 



The mechanical adhesion of the bodies of seed-plants which 

 would make parasitism possible, might be brought about in 

 three different ways. The roots growing thickly interlaced in 

 the soil might unite or penetrate each other, or adventitious 

 roots arising from internodes at any place on the aerial stems 

 might pierce the bodies of other plants, or seeds lodging in the 

 bark or in the wounds of a plant, might germinate and send 

 absorbing organs into the tissues of the possible host. Of these 

 methods, that of incidental root-parasitism seems to bear the 

 greater probability of occurrence, and to be illustrated by some 

 very striking examples. Pee-Laby has recently described a case 

 in which the main root of a plant of a passion-flower vine {Passi- 

 ftora coerulea)had become attached to a root of Japanese burning 

 bush {Enonymus japonicus) forming a specialized absorptive 

 tissue, and undergoing general atrophy of its own root-system, 

 in a manner suggestive of a highly developed degree of parasitism, 

 although but little indication of this was to be seen in the shoot 

 of the Passiflora (Rev. Gen. d. Bot. 16: 453. 1904.). 



The germination of seeds on the bodies of other plants might 

 result in mechanical parasitism, the advantage being purely one 

 of position with respect to light, and this is illustrated by many 

 hundreds of examples particularly abundant in tropical forests. 

 The development of any form of nutritive dependence out of 

 such purely mechanical relations has not yet been demonstrated 



