1917] 
FREIBERG—MOSAIC DISEASES 193 
manner described for tobacco, or the seed was sown directly 
in the paper boxes, as was the case with the cucurbits. Later 
in the season seeds were also planted directly in the soil. 
During the growing season the plants were cultivated with 
the greatest care in order to avoid injury. All plants which 
were damaged were either discarded or labeled so that any 
inconsistency in results might receive its proper explanation. 
The cucurbits grown included 2 varieties of pumpkins, 2 
of squash, 2 of watermelon, 2 of cucumber, and 1 variety of 
citron, muskmelon, and cassaba. At the end of 2 months, 
when the plants had developed several runners, inoculations 
were made with an extract from diseased cucumbers. In 
cases where runners were numerous, 3 or 4 inoculations were 
made on the same plant, the total on all varieties summing 
up to 213. Not a single infection resulted from these inocula- 
tions. 
Before offering an explanation it will be necessary to give 
some details regarding the preparation of the extract. For 
this purpose 500 grams of highly diseased shoots were gath- 
ered from diseased cucumber plants. The material was first 
washed in tap water and then rinsed in distilled water. 
Maceration was effected by placing portions of this material 
in a large mortar and pounding, crushing, and grinding the 
leaves and stems until all had been reduced to a pulp. The 
juice was then expressed through a cloth, and the residue 
washed with water until the original extract and the washings 
totaled 500 ce. An attempt was then made to filter off the sub- 
stances suspended in the extract; but due to exceedingly slow 
filtration, other means had to be resorted to. An asbestos 
mat was therefore deposited in a Buchner funnel, which in 
turn was connected with a filter flask and filter pump. The 
filter, however, soon became clogged and filtration was not 
effected with the desired rapidity. The entire extract, as- 
bestos and all, was therefore placed in centrifuge tubes and 
centrifugated until all the suspended material had been de- 
posited. The supernatant liquid, which was of a slightly 
greenish color, was used for inoculations. About fifteen hours 
