286 Transactions British Mycological Society. 
nature of the toxic substance, a supposition which was com- 
pletely demonstrated by the second series of experiments when 
the dialyser was employed. 
In a third set of experiments hanging drops of the filtered 
liquid were used, into which were stirred some mesophyll cells 
obtained by gently scraping the upper surface of a Michaelmas 
Daisy leaf with a flamed scalpel in a little distilled water. In 
this way it was possible to watch the effect of bringing the 
assimilating cells of the host into direct contact with the toxic 
substance produced by the parasite. After twenty-four hours 
it was noticed that the chloroplasts of certain cells had altered 
in position. Instead of lining the longer walls of the palisade 
cells, they were more numerous towards one or both ends of 
such cells, so that a gap devoid of chloroplasts appeared either 
at one end or at the centre. The migration of the chloroplasts 
went on until at the end of three to four days they were massed 
together at one or both ends of the cells, but were still quite 
distinguishable one from another. During the next few days 
the chloroplasts slowly lost their shape and colour; and by the 
end of the sixth or seventh day had become an irregularly 
shaped bright yellow mass. At about this time the cells com- 
menced to plasmolyse indicating the death of the protoplast. 
Thus it would appear from these observations together with 
those on inoculated plants, and on the cut shoots placed in the 
filtered culture liquid, that the first outward signs of disturbance 
—the mottling—is due to the action of a toxin on the assimi- 
lating tissue, and corresponds with the migration of the chloro- 
plasts, whereby a space devoid of these bodies is left in a large 
number of cells. The final bright yellow appearance of the 
leaves, so typical of wilt diseases, is due to the yellow fused-up 
mass of chloroplasts at the ends of the palisade cells. 
REFERENCES. 
(1) JouNnson, J. Fusarium Wilt of Tobacco. Journ. Agric. Res. xx, No. 7, 
1921, p. 519. 
(2) CROMWELL, R. O. Fusarium Blight of the Soy Bean and the Relation of 
Various Factors to Infection. Agric. Exp. Sta. Nebraska. Bull. 14, 
1919, p. I4. 
(3) Hutrcuinson, C. M. Rangpur Tobacco Wilt. Mem. Dept. Agric. India, 
1913, I, No. 2. 
(4) Younc, H.C.and Bennett, C. W. Studies in Parasitism in the Fusarium 
Group. Abs. in Phytopathology, XI. 1921, p. 56. 
