DANIEL'S EXPERIMENTS AND CONCLUSIONS 169 



1. The size of the vegetative organs of stock and cion may be 

 modified. If a herbaceous plant is grafted on itself, the general 

 nutrition is interrupted in inverse proportion to the activity of the 

 cambium layer at the time the operation is performed. The same 

 principle applies in the case of grafts between different plants of 

 the same variety. 



In the case of grafts between plants of different varieties, species 

 or genera, the reciprocal reactions are much more complicated by 

 the imperfect functional adaptations. In herbaceous grafts the 

 callus has the same effect on the cion as would placing it in arid 

 soil it is dwarfed. In determining what species of the same 

 order may be successfully grafted, similarity of habitat is of more 

 importance than relationship. In the case of ligneous plants, geot- 

 ropism (219) is a cause of variation, although this has generally 

 been denied heretofore. It is also shown that a branch that has 

 lost its negative geotropism does not always regain it if grafted on 

 the main axis of the stock, at least in the case of the pear. 



2. The flavor of the edible parts, size, chemical composition or 

 season of development, may be modified. If the union is perfect, 

 grafting in general produces a change of flavor in the edible parts 

 of vegetative organs, either in the nature of improvement or de- 

 terioration in quality. There is almost always a reduction in size 

 of the part which sometimes fails entirely to develop in edible 

 form. For the operation to have practical interest, the diminution 

 in size must be compensated by increase in quality. When the 

 edible parts belong to the reproductive organs, grafting herbaceous 

 plants may or may not cause the enlargement of the pericarp of 

 fleshy fruits or of the seeds in dry fruits. There is no known prin- 

 ciple .of general application. The flavor of the fruit depends 

 mainly on the completeness of the union and the quantity of sap 

 the cion receives. This principle applies to ligneous and her- 

 baceous plants alike. 



3. The development of the reproductive organs of the cion may 

 be accelerated or retarded. The flowering season of the cion may 

 be affected very differently, according as the plant is annual, bien- 

 nial or perennial, according to the age and nature of the cion, 

 and according to the kind of graft employed. Grafting may induce 

 variation in the arrangement of flowers, in the season 'of opening 

 or falling of the petals, or in their color. 



4. The relative resistance of stock and cion to parasites and 

 other injurious organisms or substances may be modified. The 

 principal parasites that attack grafts before the union is com- 

 plete are molluscs, worms, sowbugs, insects and molds. These 

 parasites may affect stock and cion differently. The parasites 

 that attack grafted plants after the union is complete, are in the 

 order of the extent of their ravages, insects, myriapods, fungi, and 

 other vegetative parasites, and molluscs. The more imperfect the 

 union of stock and cion, the more serious are the attacks; so 

 much so that their extent and severity may be said to be a cri- 

 terion of the degree of perfection of the symbiosis. 



