The Besting Spores of the Potato Fungus. By W. G. Smith. 123 
It will be observed there is a little difference in size between 
my oogonia (Fig. 5) and those copied from the 'Journal of the 
Eoyal Horticultural Society ; * this is because the figures in the latter 
are somewhat incorrect. When the actual sjC)ecimens are examined 
and measured side by side they are in every way identical. 
Mr. Berkeley has also most obligingly sent me a specimen of 
another (new species ?) of Artotrogus, found in decayed Turnip by 
Mr. Broome in 1849. Here the threads and semi-mature bodies 
are in the same style as the oogonia and threads from the Potato, 
and the mature spore is not truly echinulate ; it is globular, with a 
slight tendency to an oval shape, and is covered with warts. It is 
probably the resting spore of Feronospora parasitica, the pest of 
the Cabbage. 
In Figs. 4 and 2 are given copies of the oogonium and 
antheridium of Feronospora umbelliferarum and F. alsinearum, 
enlarged from De Bary to the same scale as the other figures, 
to show the close similarity in size and habit. 
Since this subject has been made public Mr. Carruthers has 
kindly furnished me with a copy of Dr. Farlow's paper on the 
Potato Eot, extracted from the * Bulletin of the Bussy Institution,' 
part iv., a paper I had not previously seen. As some of Dr. 
Farlow's practical observations seem to have a direct bearing on 
some of the points raised by me, I will conclude by extracting one 
or two sentences : " The disease is first recognized by brown spots 
on the leaves " (p. 320). " If we examine any Potato plant affected 
by the rot, even before any spots have appeared on the leaves, we 
shall always find these threads in the leaves, stem, and, in fact, 
nearly the whole plant " (p. 322). " The Peronospora is much 
more easily affected by moisture than the Potato plant itself," 
" Suppose the temperature to keep equally warm, and the atmo- 
sphere to become very damp, then the absorbing power of the 
mycelium is very much increased, while the assimilating power of 
the leaf-cells is little altered. Thus it happens that a sudden 
change from dry weather to moist will cause the mycelium to 
increase so very much beyond the power of the Potato plant to 
support it, that in the struggle for existence the latter blackens and 
dies." When the disease has arrived at a certain point, viz. just 
about the time of the appearance of the spots on the leaves, these 
mycelial threads make their way into the air " (p. 323). 
I give in conclusion an illustration of the perfectly mature resting 
spore of Peronospora infestans, as seen imbedded in the substance 
of the Potato leaf (PL CXYI.). These resting spores, which carry 
on the winter life of the fungus, are not restricted to the leaves, for 
I find them sparingly in both haulm and tuber, although I have at 
present seen the best specimens in the leaves. The engraving given 
