1916] 
GILMAN—CABBAGE YELLOWS 73 
were first grown in the greenhouse and then placed in the in- 
cubator at 22-24^C., the disease appeared in but four days, 
a period that was shorter than had been noted in any other 
experiment. This trial was repeated on March 9, and again 
the seedlings showed the disease in four days, on March 
13. Hight pots of seedlings were used, and the disease ap- 
peared in all the pots on the same day, although not all the 
seedlings in any one pot were yellow at this time. Previous 
to the appearance of the yellows, platings made from the roots 
by the hydrogen-peroxide method gave negative results in all 
eases. Further, the roots were washed out of the soil and 
examined carefully under the microscope, but no hyphae of 
the fungus were observed until after wilting or yellowing had 
begun. The rotting usually began at the tips of roots near 
the surface of the soil, and progressed toward the main roots 
and stem. The only explanation that seems applicable to 
these conflicting results is that, because the temperature in 
the greenhouse at the Garden is slightly higher than that 
found on the outside of the potting-shed, the fungus may enter 
to a limited extent, but cannot affect the host unfavorably ex- 
cept at the higher temperature, while at Madison it was un- 
able to gain any sort of a foothold. This view is further 
supported by the fact that a few plants grown in diseased soil 
in this greenhouse, after a long period of time showed yel- 
lows, as previously mentioned. 
Because the small number of hyphae found in any single 
diseased stem seemed insufficient for the blocking of the pas- 
sage of water to the leaves of the diseased plant, some pre- 
liminary work was undertaken to find, if possible, whether 
mechanical or chemical killing of the stem might bring about 
symptoms in the leaves similar to those produced by the fun- 
gus, and especially with regard to the production of a toxic 
substance to which the symptoms might be ascribed. 
To test this question six plants of cabbage were cut on one 
side with a scalpel so that half of the stem was removed for 
a distance of 0.5 em. The plants were about two weeks old 
and growing rapidly. The cut surfaces were covered with 
paraffin to prevent too rapid drying of the tender tissues. Two 
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