90 
K. M. Curtis. 
A CONTRIBUTION TO THE LIFE-HISTORY AND 
CYTOLOGY OF SYNCHYTRIUM ENDOBIOTICUM 
(SCHILB.) PERC1VAL, THE CAUSE OP 
POTATO WART DISEASE. 
Bv K. M. Curtis, M.A., M.Sc. 
Preliminary Notice. 
A N investigation of the life-history and cytology of Synchytrium 
endobioticum, the cause of Wart Disease in potato, has been 
carried on by the writer for several years. As it may be some 
time before the full results of the research can be published it 
seemed advisable to make a statement of the main results attained, 
which accordingly are embodied in the outline of the life-history 
given below. 
The stage of the organism which is most commonly observed 
is that of the resting sporangia, one of which, in cases of heavy 
infection, may occupy each cell of the three or four outermost 
layei '9 of tissue of the tumour. The sporangia continue their 
development after the decay of the host plant and eventually give 
rise to numerous uniciliate zoospores. After a period of motility 
the zoospore enters an epidermal cell of any actively dividing region 
of eye, stem or leaf, passes to the lower end of the cell, and there 
rapidly enlarges. As the result of infection a two-fold effect is 
produced on the neighbouring cells. The ring of epidermal cells 
actually in contact with the infected cell grows out to form a rosette¬ 
like structure consisting of elongated, curved cells which arch over 
the parasitised cell at their base. The other cells in the neighbour¬ 
hood divide repeatedly and a somewhat cup-shaped tumour is 
produced, at the bottom of which lies the infected cell with its 
rosette. Fresh infection frequently takes place at this stage, and 
the tumour eventually becomes a more or less spherical mass of 
tissue with the surface thrown into innumerable ridges. Passage 
of the organism from one host cell to another was never observed. 
By the time the parasite has grown to a size sufficient to fill 
the lower half of the cell it has developed a firm envelope. The 
uninucleate contents, surrounded by a thin membrane, now push 
up through a small area of the free surface of the envelope and 
