The Making of Parasites. 209 



although various workers, notably Peirce, have made extensive 

 demonstrations of the possibility of short-lived annuals, complet- 

 ing their entire cycle of existence as parasites upon enforced 

 hosts, in the tissues of which their seeds were germinated, or were 

 set at an early stage of their existence. 



Grape culturists in France sometimes insert seeds of the vine 

 in old living stems of the same plant a short distance above the 

 ground, and its results that the developing plantlets send roots 

 through the tissues which eventually reach the soil and ramify 

 in it. Many of the phenomena consequent upon grafting opera- 

 tions also are of interest in this connection. Such unions may 

 be of all degrees of intimacy, varying from perfect grafts where 

 the vessels unite, to other cases in which the cion is separated 

 from the stock by a layer of dead tissue, through which there 

 can be no free interchange of material as between a branch and 

 a main stem, but instead, a phase of parasitism exists. These 

 arrangements, in fact, present the simplest acco nplishments of 

 parasitism artificially produced. 



A large number of instances are known in which the cion 

 after uniting with the stock, or during the process, sends out ad- 

 ventitious roots, which strike downward and penetrate the 

 tissues of the host, simulating parasitis n mechanically, as 

 would be done whenever the roots of any plant accidentally 

 bore through those of another. No real or important transfer 

 of food material has been demonstrated in such cases, and the 

 roots showed no prolonged existence. 



In the organization of an experi iiental analysis of the condi- 

 tions of parasitism, at the Desert Laboratory, it was thought 

 advantageous to use plants furnished with a large water- balance, 

 and hence capable of existence for extended periods, independent 

 of any additional supplies. Such forms have great inertia, that 

 is, cuttings or sections of the body may carry on existence in a 

 fairly nonr al manner for a long time, without additional supplies, 

 and during this time, regeneration and the formation of new 

 absorbing organs m.ay take place with adjustment to conditions 

 of parasitism. Observations of material of this character might 

 well furnish exceptional opportunities for detecting the con- 

 junction of conditions, or developing stages which would facili- 

 tate the assumption of dependent relations in nutrition. The 



