148 THE PLANT WORLD 



transmitted at all through the seeds. The other type of 

 variegation is a normal inherited quality transmitted to the 

 offspring just as any other normal quality might be. The 

 latter type of variegation is not at all infectious. 



It has been known to gardeners for 200 years that the 

 grafting of a variegated cion into a green-leaved stock may 

 make the latter variegated through "graft infection," and 

 ■vice versa, that a green cion set into a variegated stock is 

 apt to become variegated. The most familiar cases of this 

 kind are found in the Malvaceae, in which a considerable 

 number of variegated varieties have now been formed 

 through the infection of different species by means of graft- 

 ing. All of these varieties among the cultivated Malvaceae 

 are traceable to a single variegated specimen of Abiitilon 

 striotinn Dicks., which was introduced into Europe from the 

 West Indies by James Veitch & Son in 1868 and distributed 

 under the name Ahutilon Thovipsoni. 



All efforts to produce an infection by any means other 

 than grafting have thus far proved futile and it seems 

 evident therefore that the infection is not due to an inde- 

 pendent organism. Dr. Baur concludes that the infecting 

 substance is a toxin produced by the diseased cells. The pro- 

 duction of this toxin is in large measure dependent upon 

 sunlight. Specimens growing in the shade are much less 

 variegated than those growing in bright light. The disease 

 may be completely cured by removing all variegated leaves 

 and setting the plants for some time in diffused light. When 

 again brought into bright light no more variegated leaves 

 will be produced. If a single variegated leaf is left on the 

 plant, however, or if a single variegated leaf is grafted 

 into it, the whole plant will be very soon reinfected upon 

 removal to strong light. The cure of the plant by the 

 shade treatment is absolute with respect to all the new 

 growth, but if by cutting back or other means a bud is 

 caused to develop which occupied the axil of a variegated 



