THE ORIGINATION OF PARASITISM. 57 



stance from the host wholly foreign to it. These deviations from the 

 normal are accompanied by functional performances, in respiration, photo- 

 synthesis, and various types of catalytic action of unusual rates indicative 

 of serious correlational disturbances. 



The movements displayed by the etiolated and greened slips of Opuntia 

 which were used in the experiments were marked and long continued and 

 are not surpassed in interest by anything revealed by the present investi- 

 gation. These shoots were allowed to continue in an etiolated condition 

 for several months, thus allowing the non-differentiated tracts of tissue to 

 undergo some of the changes toward maturity; and then after these were 

 so well forward as to admit of but little change, were exposed to the light. 

 The thin, flattened stems were flexible and immediately began to give out 

 branches of the usual broadly ovate type of the normal plant. Being 

 now established in parasitic relations with Echinocactus , in which no root- 

 systems were formed, a novel form of nutation was set up, not accompanied 

 by growth, since the shoots displaying it did not increase in length when 

 calibrated to 0.1 mm. Furthermore, the curvatures were as pronounced 

 in the older basal portions of the stems as in the younger. These curva- 

 tures appeared in one flank of the stem at the tip, and this zone would then 

 slowly slide down to the base, after which it would be transferred to the 

 opposite flank and pass upward to the apex, the total cycle including about 

 three days. At present no such movement has been seen in similar stems 

 rooted in the soil, though few specimens have been examined. If simi- 

 lar movements in any other plants have been found, their record has not 

 been seen by the author. 



These movements are seen to be produced by the action of the "cortical" 

 parenchyma, which makes up two-thirds of the shortest diameter of the 

 stems. Shortly after the attainment of full size, decortication is begun 

 by shrinkage of this parenchymatous tract, with the result that the walls 

 become various-folded and the epidermis wrinkled. The reduction of the 

 turgidity and the collapse of the cells takes several months, and it is dur- 

 ing this period that the movements are manifested. It can not be deter- 

 mined definitely whether the curvatures are produced by the formation of 

 zones of increased turgidity on the convex side or by lessened pressure on 

 the concave side. The inequality is sufficient, however, to carry the tips 

 of the stems through an arc of 180 with a fairly regular period of about 

 70 to 72 hours. This movement is illustrative of the reactions which bear 

 no direct or accommodative relation to the factors producing them. 



In any attempt to summarize the facts bearing upon the entire subject 

 of dependent nutrition as an adjustment or "adaptation," it is first to be 

 recalled that the couplings of portions of the shoots of species of marked 

 morphological unlikeness in grafting operations often result in adhesions, 

 in which the adjustment of nutrition constituting partial parasitism is 

 initiated in its least pronounced form. 



