FILTERABLE VIRUSES* 



The so-called filterable viruses, today generally called merely viruses, 

 are still of unknown affiliations so far as relationships to established groups 

 of microorganisms are concerned. They are treated here as members of 

 an order, consisting of 13 families, 32 genera and 248 species. 



Among viruses as we know them, there are three constituent groups 

 that have come to be recognized, and to some extent named and classified, 

 through the largely separate efforts of bacteriologists, animal pathologists, 

 and plant pathologists. Taxonomic overlappmg of the three groups, 

 viruses affecting bacteria, viruses having onlj'- animal hosts, and viruses 

 invading higher plants, can hardly be justified as yet by available evidence. 

 Nevertheless it has been shown that a single virus may multiply both in a 

 plant host and in an insect vector. This seems to dispose of the thought 

 that adaptation to a plant or animal enviromiient would necessarily pre- 

 clude utilization of other sources of the materials needed for multiplication. 



For the present it seems feasible to continue \\dth the custom, tacitly 

 accepted in the past, of classifying bacteriophages separately as one 

 sub-group, \-iruses causing diseases in seed plants as a second sub-group, 

 and those causing diseases in animals as a third sub-group. It should be 

 recognized that this may prove to be only a temporary arrangement, 

 necessary because we have no evidence to warrant taxonomic overlapping 

 of the three groups and useful while we await critical investigations and 

 possible development of a substitute plan capable of displaying natural 

 relationships to better advantage. Eventually evidence may become 

 available to show that some bacteriophages can infect higher plants or 

 anmials and can mcrease in the new envirormient, or that viruses known 

 to attack anmials or plants can similarly enlarge their host ranges. Or, 

 there may be discoveries of common physical properties that would aid 

 in formulating an interlocking classification, for which at present we lack 

 any substantial basis. 



It is of especial significance now that the three fields be unified at least 

 by a parallel development of nomenclature. Toward this end the pres- 

 ent section of this supplement is directed. 



* Supplement No. 2 has been prepared by Francis O. Holmes, The Rockefeller In- 

 stitute for Medical Research, Princeton, N. J., September, 1944. In this section, 

 authorities for the names of plant hosts are in general as given by Gray's New Manual 

 of Botany, 7th edition, and Bailey's Manual of Cultivated Plants, 1938 ; in each of these 

 standard works will be found a list of abbreviations customarily used in botany in citing 

 authorities for binomials. 



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