Virus multiplication was usually unaffected by the presence of a nitrogenous
source in the solution, with
or without sucrose and phosphate. In one typical
experiment with solutions containing
10 g. sucrose/l. and 0.2 g. calcium
phosphate/l., the
mean yield of virus in sap for two replications was 1.45 mg./
ml. with ammonium sulphate, 0*2g./l. and
1-40 without it. In a few experiments
the addition of nitrogen decreased virus concentration and in a few made in
the summer increased
it.
Increases occurred with leaves taken from plants
showing signs of nitrogen deficiency, and in such leaves virus production was
increased by sucrose and phosphate only when nitrogen was added. The way
in which the nutritional state of the plants at the time of inoculation influenced
the effects
of nutrient solution on the virus multiplication was shown by experi-
ments with plants given different nutrients. Half of one group of nitrogen-
deficient plants were given ammonium sulphate
1 g. per pot 2 weeks before
inoculation. Half
of the inoculated leaves in each group were placed in water
and half in a solution containing sucrose and calcium phosphate. The con-
centration
of virus in sap from the plants that received ammonium sulphate
was (mg./ml.):
0.3 Erom leaves in water and 1-0 from leaves in solution; from
the plants which
did not receive ammonium sulphate 04 from leaves in water
and
0-6 from leaves in solution.