68 ESTABLISHMENT OF VARIETIES IN COLEUS 



In the infectious variegation of the type seen in Abutilon striatum 

 thompsonii the pattern is a mottled one, with irregular yellowish areas 

 mingled with the green. The amount of yellow varies considerably, 

 especially according to intensity of illumination. In Abutilon mega- 

 potamicum variegatum especially the distribution on a single plant is 

 very irregular (see Reid, 1914). Only a few blotches may appear on 

 a leaf and often entire leaves or all leaves on an entire branch may 

 be pure green. Baur (1906a) found green branches on Abutilon striatum 

 thompsonii and was able fully to establish that they were immune. 



Immune branches arise on a plant as bud variations, but the leaves 

 differ from those with variegation only in having all cells immune, for 

 in the latter a part of the cells perhaps remain immune. It may be 

 noted that blotched variegation in this case either results from irregular 

 immunity or to irregular distribution of virus, and hence emphasizes 

 the intercellular relations concerned with distribution. 



Whatever the nature of the "virus" may be, it is fully demonstrated 

 by Baur that it is a product of the diseased cells of the old leaves and 

 is transported to j^oung leaves in which certain areas of cells succumb 

 to the influence while others do not. This immunity exhibited by 

 some cells, however, may suddenly extend to entire leaves or to all leaves 

 on a branch. As to the flow of the " virus," Baur (1906o) found that 

 it could pass through tissues of immune strains of Abutilon arboreum, 

 causing infection to non-immune parts beyond, but that such infection 

 was not produced if immune tissue of Lavatera arbor -ea intervened. 



It should be noted that this type of variegation can not, as far as we 

 know now, be distinguished by appearance from other types of mottled 

 variegation. Its infectious nature and the failure to transmit to seed 

 progeny are the characteristics of these cases. As noted above, 

 Shull (1914) suggests that certain yellow-flecked types of variegation 

 giving very irregular transmission to seed progeny may be of such 

 infectious nature that it can be carried in some of the germ-cells. 

 It may well be that in many cases of variegation (especially of the 

 blotched types), the disturbing cause producing loss of chlorophyl 

 may be quite similar in nature to that of the vigorously infectious types. 

 In the latter it is quite clear that the production of a " virus" in varie- 

 gated leaves and its flow to young leaves does occur. 



Differences in the extent of influence of such a "virus" may give in 

 some types an apparent inheritance through seed progeny. In the 

 infectious types we know nothing definite concerning the appearance 

 of variegation in the plant first showing it. It appears (Reid, 1914) 

 that many, if not all, of the abutilons with infectious variegation arose 

 through grafting with one original strain, Abutilon striatum thompsonii. 

 The presence of infectious variegation in such widely differing genera 

 as Nicotiana, Fraxinus, Abutilon, and Ligustrum indicates that the 

 condition should arise spontaneously. Frequent and almost continued 



