ГУоп, 4 
204 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
chlorotic. The plant was therefore removed to the green- 
house in spite of the danger of freezing. On January 16, it 
was noticed that the plant had been severely chilled and that 
the edges of nearly all the leaves were turning black. The 
three shoots referred to above were removed, macerated in 5 
ec. of distilled water, and the extract used for inoculations. 
The shoots weighed from 1.5 to 2 grams. Checks were run by 
inoculating plants with the juice of healthy tobacco plants 
and with sterile tap water. Ten plants were used in each case. 
No infections whatever occurred, and this is particularly 
significant since all extracts gave a strong oxidase reaction 
with guaiacum and hydrogen peroxide. 
It would therefore seem that during the time which elapsed 
between the chilling of the plant and making the inoculations, 
the metabolism of the plant had been altered sufficiently to 
destroy the infective principle which the shoots originally 
contained. One can readily conceive of such an alteration, if 
we accept the enzymic theory as an explanation of the cause 
of the disease. The mottled shoots which had remained on 
the old stalk lost the sharp definition between lighter and 
darker areas, and the green shaded gradually into the lighter 
areas, the general position of which was marked by a yel- 
lowish brown spot. These results also show that the infective 
substance is not found in the tissue of normal plants. 
Recovery from mosaic has been denied by many workers, 
and we are not in a position at this time to state that the ex- 
periments reported above demonstrate actual recovery. The 
failure of most workers to observe anything in the direction 
of recovery of diseased plants may probably be accounted for 
by the fact that the work on this phase of the problem has 
been rather limited. Some work in this direction has been 
done by liming the soil, ete., but no elaborate experiments 
have been performed. The work has furthermore been done 
under environmental conditions which favored the develop- 
ment of the disease. We may rest assured that when plants are 
grown under such conditions that the spontaneous appearance 
of the disease is favorable, recovery from the malady will be 
exceedingly rare. This applies particularly to greenhouse 
