49 
The principal point is that the fungus I have especially studied 
leads the way for these purely saprophytic anaérobic and aérobic 
forms into the tuber: once in the mature tuber, its progress is 
necessarily slow until the reserves move in the spring. 
During the past winter I gave to Miss Dawson, who is working at 
such subjects in my laboratory, some of the tubers saved from plants 
attacked with this disease, to investigate the various fungal forms 
lurking in the diseased tubers. Her investigations are not yet com- 
pleted, but enough has been accomplished to convince us that after 
the fungus in question has opened up the way into the tuber, all 
sorts of bacteria and fungi can make their way down the destroyed 
vascular strands, and reappear in spring, when the tubers are replanted. 
But this is not all. The evidence shows that the fungus in 
question, once in the tuber, leads a dormant life during the early part 
of the winter, but gradually invades the new sprouts as they slowly 
appear in the early spring, and that the parasite is actually replanted 
by the farmer or gardener, when restocking the ground, in his new 
sets.” 
If we reflect that the tuber is really a bud, there is nothing 
especially strange in this phenomenon; the fungus enters the base 
of the bud in autumn, and takes some months to traverse its dormant 
tissues during the winter and spring. A spotted tuber may give rise 
to some healthy and some diseased sprouts, according to the tracks of 
the fungus. 
A curious phenomenon was observed in some potato plants very 
badly attacked by this disease this summer. In some of the badly 
diseased young shoots quantities of beautifully developed cubical 
_ protetd crystals (crystalloids) were observed in the parenchyma of the 
pith and cortex. It is due to Mr. W. G. P. Ellis to point out that 
he was the first to see these in some sections he was kindly cutting 
for me of this batch of specimens. On going further into the matter 
I find such crystalloids have been seen by Heinricher in the shoots 
of a diseased potato (1), but he did not give any account of the 
disease itself. 
I find these crystals are not uncommon in the still green bases of 
/ 
the petioles of the withered leaves hanging on the diseased shoots, 
though they do not always occur. 
T ascribe their formation to the accumulation of proteids in the 
(1) Ber. d. deutsch. bot. Ges. 1891. 
