182 



L. M. BLACK 



plant, and animal viruses would have to be replaced eventually by some more 

 basic classification. 



Bawden (Black, 1953b, p. 413) considered that the demonstration of virus 

 multiplication in both plants and insects favored their symptomless insect 

 vectors as their origmal evolutionary source. This concept has been expanded 

 by Maramorosch (1955). He pointed out that the insect vector host 

 range is narrow, comparatively speaking, and the plant host range usually 

 quite broad and believed that this, as well as the lack of symptoms in the 



Fig. 1. Schematic representation of the life cycle of wound tumor virus. Clear drawings 

 represent virus-free hosts; stippled drawings, hosts in which virus increase is occurring; 

 black drawings, fully infected hosts. The right half of the circle represents virus 

 propagation in the plant; the left half, virus propagation in the insect vector. The latter 

 phase may be repeated directly by transovarian passage of virus. (Modified from Black, 

 L. M., 1951, in Brooklyn Botanic Garden Ann. Kept, for 1950-1951: 32-33. Drawing by 

 Natalie H. Davis.) 



