[Vor. 4 
192 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
stance naturally ‘‘toxic’’ to a plant might, even in extreme 
dilution, cause serious metabolic disturbances. During the 
time that the above work was deferred on account of another 
phase of the problem, an article was published by Allard 
(716%) on some of the properties of the infective principle 
which showed conclusively that the mosaic disease of tobacco 
is not caused by oxidases but, according to Allard’s interpre- 
tation, is caused by an ultramicroscopic parasite. The 
writer’s preliminary work substantiates the more elaborate 
experiments of Allard, thus eliminating oxidases as a cause 
of the disease. I do not, however, concur with him in the in- 
terpretation of the properties of the infective principle, as 
will be noted later on. 
Piotr EXPERIMENTS 
A great deal of interest has been aroused recently by the 
mosaic diseases of cucurbits, particularly of cucumber. Dur- 
ing the spring of 1916 cucumbers grown in the experimental 
greenhouse contracted the disease, and an experiment was 
planned to test its transmissibility not only to other cucur- 
bits but also to other plants susceptible to the malady. All 
seeds were started in the greenhouse and later transplanted 
to the plot. 
Injury to seedling at the time of transplanting has often 
been cited as predisposing plants to the disease, and it there- 
fore became desirable to eliminate this factor. Tobacco seed 
was sown in flats and after 10 days the seedlings were trans- 
planted to small paper boxes. The cotyledons had just ex- 
panded at the time of transplanting, and the entire plant 
measured about 4—3 inches in length. Although exceedingly 
small, the seedlings could be handled without injury other 
than probably the destruction of a few root hairs. The paper 
boxes to which the plants were transferred were 24 inches 
long, 14 inches wide, and about 2 inches deep. When the 
plants were large enough to be transplanted to the plot, the 
entire box was submerged in the soil. This eliminated all 
possible chances for injury. Tomato seedlings were obtained 
by planting the seed in flats and handling the seedlings in the 
