174 
THE FLOBIST AND POMOLOGIST. 
[ August, 
seen, measured and illustrated, but till now the resting-spore of tlie 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 Soutli-American species of Solarium ) we should then find 
plenty of resting-spores. It grows on various species of Solarium besides S. tuberosum; it is 
even not unfrequent on the woody Nightshade of our hedges, and it grows upon the Tomato 
and other Solanaceous plants. On these latter, however, it makes less headway than upon 
the Potato. As an instance in point, the allied pest of the garden Lettuce —Peronospora 
gangliformis —may be mentioned. Here, if tlio 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-sporos 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 Solanacece to find the resting-spores in any 
abundance, yet, as the resting-spores of the Lettuce-mould can by searching bo found in the 
Lettuce itself, so the resting-spores of the Potato fungus have without doubt this year been 
found in the Potato plant. 
Fig. 2.—Peronospora infestanS: Oogonia and Antheridia from badly diseased leaves of Potato after a 
week’s maceration in water, enlarged 400 diameters. 
“ How this came about is now pretty generally known. Mr. Murray exhibited some speci¬ 
mens 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 
freo, as the coat of cellulose disengages them from the mycelial threads. But some similarly 
spotted leaves had been previously sent to me, 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 these circular bodies out of the leaves and stems, by maceration in 
water, I found that the moisture greatly accelerated the growth of the mycelium, and that 
tho 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 soarcliing, I 
could only find ono or two. Afterwards I found them more abundantly in different stages of 
maturity, especially in the very putrid stems and in the tubers when in the last stage of 
decomposition. Mr. Berkeley afterwards found thorn with abundant mycelium.It is 
quite possible that the condition of the Potato, as seen during the present season, is quite 
exceptional, and that it may not occur again for a long series of years. 
“In fig. 1, which is an exact copy of the first sketch taken, the oogonia and antheridia 
