GRAFTING AND GRAFT-HYBRIDS 175 



be produced by injecting the sap of a diseased plant into a healthy one. 

 The same result was produced when the sap was rendered free of germs 

 by filtration through unglazed porcelain, and hence the action is apparently 

 due to some substance of the nature of a ferment, which is destroyed by 

 boiling but not by drying or by alcohol. Beyerinck was, however, unable 

 to produce any variegated foliage upon other healthy plants by injecting 

 them with the sap from albicant varieties. Possibly the mode of exchange 

 or of the application of the stimulating metabolic product may have the 

 same importance as in the production of certain galls. 



It is possible that all the observed symbiotic reactions are the result 

 of irritable responses of the symbiont: affected, and could be produced in 

 the absence of the exciting symbiont if the required internal and external 

 conditions could be produced by other means. For instance, many plants 

 produce variegated or albino varieties as sports, and since this abnormality 

 is favoured by unusual conditions, it is possible that the abnormal relation- 

 ship of graft and scion may induce a similar tendency. 



Vegetatively and sexually produced variations arise in the absence 

 of any symbiosis, and hence the changes produced by grafting do not 

 necessarily involve the occurrence of any protoplasmic fusion between 

 the graft and stock. This does not even follow when the properties 

 of the one symbiont appear in the other, provided that these peculiarities 

 are ones which the symbiont affected can itself develop under appropriate 

 conditions. All the cases observed hitherto in which the graft and scion 

 have shown a more or less marked tendency to morphological similarity 

 might easily be the direct result of special stimuli which induce the 

 observed changes of shape. If the term hybrid is restricted to the 

 products of protoplasmic fusion, then it is certain that the existence of 

 graft-hybrids, though possible, has not been proved. Only when the 

 meaning of the word is unduly extended to include the transference 

 of such peculiarities as variegation, however such transference may occur, 

 can the existence of graft-hybrids be granted *. 



The differences of opinion as regards the existence or non-existence of graft- 

 hybrids are due mainly to the dissimilar meanings attached to the term and to the 

 varied interpretations given to the facts 2 . Sufficient attention has not been paid 

 to the fact that the power of response may either be very great or extremely 

 lited. It is this limitation which prevents the root-system of Helianthus annuus 

 >m forming tubers and storing inulin when a shoot of H. tuberosus is grafted 

 ipon it 3 . Similarly the root-system of an annual plant cannot be made perennial 



1 Cf. Vochting, Sitznngsb. d. Berl. Akad., 1894, p. 716. 



2 Cf. Vochting, 1. c., and Daniell, 1. c. (p. 173, note 5). On Cytisus Adami Fuchs, Sitzungsb. 

 Wiener Akad., 1899, Bd. cvn, I, p. 1273 ; Beyerinck, Koninklijke Akad. d. Wetenschappen et 



| Amsterdam, 1900, p. 365. 



* Vochting, 1. c., 1894; Daniel, 1. c., 1898, p. 147. 



