DEPENDENT NUTRITION IN SEED-PLANTS. 6 



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 accomplishments 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 adventitious roots, which 

 strike downward and penetrate the tissues of the host, simulating para- 

 sitism 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 have 

 shown no prolonged existence. 



In the organization of an experimental attack on this problem 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 normal manner for a long time without additional supplies, 

 and during this time regeneration and the formation of new absorbing 

 organs may take place with adjustment to conditions of parasitism . Obser- 

 vations on material of this character might well furnish exceptional oppor- 

 tunities for detecting the conjunction of conditions or developmental stages 

 which would facilitate the assumption of dependent relations in nutrition. 

 The use of massive plants also rendered it easy to make the chemical analy- 

 ses necessary to determine the concentration of the cell-sap, which was 

 thought to be of importance in this connection. 



The most direct method of ascertaining the relative osmotic value of the 

 sap of two plants would be by freezing-tests of the expressed juice. Sev- 

 eral of the species used in the experiments, however, contained so much 

 mucus that it was impossible to get clear solutions. Our experiments 

 therefore comprised a complete series of analyses in which the solid ma- 

 terial carried by the sap was ascertained, and in addition freezing-tests 

 were made of a number of the same plants. From these it may be seen 

 that the ash-content of the sap is not invariably to be taken as an index of 

 its osmotic activity. 



The results of similar examinations of host and parasite are not acces- 

 sible to the author, and it is doubtful whether such comparisons have been 

 made before. Paul Reinseh compared the constituency of Viscum album 

 with Pinus sylvestris upon which it was growing, obtaining the result that, 

 while the soluble portion of the ash of the mistletoe was as 15 to 19 to the 

 insoluble part, the soluble part of the ash of the pine was but 15 to 47 of in- 

 soluble matter. Much of this disproportion was due to the greater amount 

 of lime in the host, while it was notable that the parasite contained a much 

 larger amount of phosphorus compounds. These data, however, have but 

 little value with respect to their bearing upon the relative osmotic activity 

 of the sap of the host and parasite, and no measurements of the concentra- 



