[Vor. 4 
208 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Tue Inrective PRINCIPLE REGARDED AS AN ORGANISM 
The work reported above was undertaken with the hope of 
obtaining information on the chemical or physiological 
nature of mosaic diseases. The problem was not, however, 
treated solely from this standpoint, but was undertaken in 
an unbiased attitude with the hope of gaining any possible 
information on all sides of the problem. А set of experiments 
was therefore planned which might bring out more clearly 
any relation of mosaie diseases to parasites or filterable 
organisms. 
One method of attack was that of growing plants under 
sterile conditions. If plants grown under sterile conditions 
contracted the disease, the cultures otherwise remaining 
clean, one would, from a uniformity of results, be justified in 
concluding first, that the disease originated within the plant 
and that it is really of a metabolie or physiologieal nature, 
and second, that we have actually encompassed all physio- 
logieal faetors necessary for its production. If, on the other 
hand, no mosaic occurred, one would nevertheless not yet be 
justified in concluding that the disease must be due to an 
organism, since we are in the first place absolutely ignorant 
of the cause of the disease, and the physiologieal faetors nec- 
essary for its production may be absent or subdued. 
The cultures were prepared in the following manner: Jars 
(measuring 20 X 8 em. and 16 X 10 em.), specimen tubes (40 
х 5 em.), cylinders (48 x 5.5 em. and 36 х 8 em.), and tall 
specimen jars (varying in size from 40 X 11 em. to about 
60 x 16 em.) were used. А certain amount of soil, the quan- 
tity varying with the size of the jar, was placed in each jar 
and a proportionate amount of water was added. All vessels, 
with the exception of the tall specimen jars, were sterilized 
for 4 hours at 15 pounds pressure. The latter were sterilized 
with formaldehyde, rinsed with sterile distilled water, and 
into them a certain amount of sterile soil was then placed. 
Soils from different sources were used, i. e., from the plot 
containing diseased plants and from greenhouse plots in 
which diseased material had been grown. Soils from the to- 
