FAMILY MARMORACEAE 1163 



FAMILY II. MARMORACEAE HOLMES EMEND. 



(Handb. Phytopath. Viruses, 1939, 16.) 



Viruses of the ^losaic Group, inducing diseases usually characterized b}' persistent 

 chlorotic or necrotic spotting, and often by mottling. The family is here extended to 

 include several small groups of viruses, formerly assigned independent family rank, 

 but sharing a tendency to aphid transmission, so far as known, and inducing diseases 

 characterized bj- abnormal growth habit, thickening and rolling of leaves, or dwarfing, 

 traits not incompatible with the characters of the present group. Should anj' one of 

 these small groups become the center of a large assemblage of new viruses in the future, 

 separate familial status for it might again be advantageous. In the combined group- 

 ing here used, specific vectors, so far as known, are aphids (APHIDIDAE). 



Key to the genera of Jamily Marmoraceae. 



I. Viruses of the Typical Mosaic-Disease Group. 

 Genus I. Marmor, p. 1163. 

 II. Viruses of the Spindle -Tuber Group. 

 Genus II. Acrogenus, p. 1202. 



III. Viruses of the Leaf -Roll Group. 



Genus III. Corium, p. 1203. 



IV. Viruses of the Dwarf -Disease Group. 



Genus IV. Nanus, p. 120G. 

 V. Viruses of the Rough-Bark Group. 



Genus V. Rimocortius , p. 1208. 

 VI. Viruses of the Symptomless Group. 



Genus VI. Adelonosus , p. 1211. 



Genus I. Marmor Holmes. 



{Loc. cit., 16) 



Viruses inducing t3'^pical mosaic diseases in various plants. Generic name from 

 Latin marmor, a mottled substance. 

 The type species is Marmor tabaci Holmes. 



Key to the groups within germs Marmor. 



A. Relatively resistant to heat inactivation, usually requiring more than 10 



minutes at 85 to 90° C for complete inactivation. 



1. Tobacco -IMosaic Virus Group. 



B. Relatively susceptible to heat inactivation, requiring less than 10 minutes at 



85 to 90° C for complete inactivation. 

 a. Replacing potato-veinbanding virus in mixed infections. 



2. Tobacco-Etch Virus Group, 

 aa. Not replacing potato-veinbanding virus in mixed infections. 



3. Cucumber-Mosaic Virus Group. 



C. Many additional species cannot yet be grouped into definite subdivisions of 



the genus ; they constitute a residual or 



4. Miscellaneous Mosaic-Virus Group. 



Key to the species of the Tobacco-Mosaic Virus Group. 



Viruses relatively resistant to heat inactivation, requiring in most cases more than 

 10 minutes at 85 to 90° C for complete inactivation. Insect vectors as yet unknown 

 under natural conditions. 



