204 III. THE EVOLUTION OF VIRUSES 



It was said that the difference between a carnivore and a para- 

 site is simply the difference between living upon capital and income, 

 between the burglar and the blackmailer, but this view may not be 

 legitimate, for there seems an essential difference between them. A 

 carnivore may eat flesh of every kind of animals, whereas between a 

 parasite and its host there is a specific relationship which should be 

 found between a virus and its host or even between an enzyme and 

 its substrate. Caterpillars feed on the leaves of plants, but there is 

 a definite relation between a caterpillar and the sort of the plant. 

 Again, there is also a specific relationship between a mushroom and 

 the kind of trees on which it grows. 



As to the plant kingdom, not only mushrooms but generally fungi 

 can be regarded as the secondary organisms. Schizomycetes or bacteria 

 may be regarded as the secondary as above stated. Likewise phy- 

 comycetes or slime fungi, at least plasmodwphorales may be so, since 

 these are especially distinct in their parasitic nature. The groups of 

 fungi proper, including phycomycetes, ascomyceies and basidioniycetes, 

 that constitute the overwhelming large phyla of the plant kingdom 

 are all parasitic to more or less extent. They may possibly be the 

 organisms having evolved chiefly from various plant viruses. 



It should be noted that most of the fungi, though prefering moist 

 locations, do not thrive if submerged in water ; but their parasitic 

 nature is marked, indicating clearly that they are never the primary 

 organisms generated and advanced in water. Among them the rust 

 fungi, protobasidiomycetes, are striking examples of obligate parasite, 

 that is, organisms unable to live except in living tissues. They are 

 incapable of living in culture media, even when the media are made 

 from the host plant upon which they thrive. 



Almost all the fungi are thus parasitic, but algae are free-living 

 although many of them are extremely primitive both in form and func- 

 tion. For example, the cyanophyta, or blue-green algae, are so primitive 

 that there is no morphological separation of nucleus and cytoplasm, 

 chromatin being distributed throughout the cell. Non-parasitic nature, 

 however, would be no gainsaying their possibility of being secondary 

 organisms. It may be highly possible that the secondary organisms 

 having been generated from higher plants, which can utilize the en- 

 ergy of sunlight by virtue of the catalytic properties of chlorophyll, 

 may also be able to do so in their extremely primitive state because 

 they may inherit the faculty from the plant. 



The fact that phyla or classes in the plant kingdom are extraor- 

 dinarily numerous and complicated, no phylogenetical correlation 

 appearing to be present among them, suggests that at least the ma- 

 jority of them may be the secondary organisms. It may rather be 



