118 The Resting Spores of the Potato Fungus. By W. G. Smith. 
now the resting spore of the Potato fungus has eluded all search. 
The reason generally given and accepted for its absence is, that 
the Potato is not the plant on which the fungus luxuriates to the 
greatest extent, and that if we only knew the plant it most affects 
(probably some South American species of Solanum) we should 
then find plenty of resting spores easily enough, for it must not be 
forgotten that the Potato fungus is by no means confined to the 
Potato. It grows on various species of Solanum besides Solanum 
tuberosum ; it is even not unfrequent on the woody Nightshade of 
our hedges, and it grows upon the Tomato and other Solanaceous 
plants, together with at least one plant which belongs to quite a 
different natural order. On these latter, however, it makes less 
headway than upon the Potato. As an instance in point the allied 
pest of the garden Lettuce may be mentioned — Peronospora 
gangliformis — first described by Mr. Berkeley. Here, if the 
resting spores of the parasite are wanted, they must not be sought 
for in the Lettuce itself, where they are only sparingly produced, 
but in a plant belonging to the same natural order also commonly 
afflicted with the same parasite, viz. the common Groundsel ; the 
resting spores are said to be even more common in Sow-thistles 
than Lettuces. 
Therefore, although it is probable we shall have yet to look to 
some other member of the natural order Solanaceae to find the 
resting spores in any abundance, yet, as the resting spores of the 
Lettuce mould can by searching be found in the Lettuce itself, so 
the resting spores of the Potato fungus have without doubt been 
found this year in the Potato plant. 
How this came about is now pretty generally known. Mr. Murray 
exhibited some specimens of Potato leaves badly diseased before the 
Scientific Committee of the Royal Horticultural Society. In the 
corroded spots of these leaves Mr. Berkeley’s sharp eye detected 
dark-brown warted bodies (but no mycelium), which he referred to 
the genus Protomyces. Assuming these bodies to be the true 
resting spores, which they doubtlessly are, they were necessarily 
free, as the coat of cellulose disengages them from the mycelial 
threads. But some similarly spotted leaves had been previously 
sent on to me, from the ‘ Journal of Horticulture,’ upon which I 
detected the old Potato fungus, mycelial threads within the leaves, 
and some circular transparent bodies of two sizes, new to me. 
In attempting to wash the circular bodies out of the leaves and 
stems, by maceration in water, I found the moisture greatly ac- 
celerated the growth of the mycelium, and that the long-sought-for 
oogonium and antheridium was at length the result. These bodies 
were at first most sparingly produced, so that for many days, and 
after most careful searching, I could only find one or two. After- 
wards I found them more abundantly in different stages of maturity, 
