72 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



remarkably according to the season where the expriments are carried 

 out. For example, the yield of tomato busy stunt virus in summer is 

 only about one fifteenth of that in winter ; with tobacco necrosis this 

 is found to be only about one twentieth. This fact may indicate that 

 in summer the combination with lipids is so firm that their expulsion 

 is hardly possible. 



According to Nixon and Watson (58) the sap from sugar beat 

 plants infected with beat yellow virus contains at least two kinds of 

 specific particles, and one of these is the rod which can be seen with 

 the electron microscope, the other probably occurring in a much 

 higher concentration, appearing to be spherical. They stated that pos- 

 sibly the rods are an alternative form of this spherical particles, 

 which can be found in large quantities in clarified sap from healthy 

 plants. This finding is what should be expected from the writer's 

 view just mxentioned. Furthermore, on an electron microscopic study 

 of tobacco-mosaic virus and some 35 other viruses, Johnson (59) found 

 some rod-like particles with tobacco-mosaic virus and with several 

 other viruses, but failed to find any rod in another large group of 

 virus-infected plants. He suggested that the rod-like particles in 

 question may be a result of disease rather than the ultimate causal 

 unit. 



It should be noted in this connection that only extremely small 

 quantities of virus particles are usually yielded from infected plant 

 saps. For example, the yield of tobacco-necrosis virus particles from 

 a litre of infective bean's sap is stated to be only 0.001 g.; the yield 

 of tobacco-mosaic virus proteins from infective tobacco plant sap 

 appears to be the highest, but only 2.0 g. (25). 



Wildman and Bonner (60), on an electrophoretic study of plant 

 virus proteins, found that a distinct fraction appeared in the sap 

 following the infection of plants with tobacco-mosaic virus ; the frac- 

 tion was detectable after 4 days of infection, and after 20 days became 

 very conspicuously. If the expulsion of lipids took place in the pro- 

 toplasm proteins, there would appear a peculiar fraction detectable 

 in the electrophoretic pattern, and therefore if the lipids expulsion 

 failed to occur, the detection of virus formation would not be accom- 

 plished by this method. Actually in the sap of Turkish tobacco in- 

 fected with curly-top virus no distinct fraction was demonstrated in 

 the pattern ; it should be realized that this virus has not ever been 

 isolated in a crystalline form, indicating that lipid-expulsion cannot 

 occur with this virus. 



Insect viruses causing polyhedrosis can be isolated on the one hand, 

 as described in a previous chapter, in rods similar to those of some plant 

 viruses, whereas on the other hand, it has been reported that there 



