165 
At Q on fig. 4 may be seen Peronospora mycelium with a young plant (qx) 
growing from amongst the starch of the Potato tuber, the dark background showing 
the cell wall corroded by the fungus, and at R a similar fragment of mycelium upon 
the cuticle of a Potato leaf ; it is very common to see one cell of the cuticle thus 
discoloured by the corrosive mycelium, the corrosion of the cell being caused by 
the mycelium passing over and upon it. Both threads here shown come direct 
from last year’s resting-spores. At s is engraved a branch of the Potato fungus, 
showing the numerous partitions with which the threads are at times furnished, 
and at T is a typical well-grown branch of the fungus, with a full-grown conidium 
at the apex ; this conidium may either discharge zoospores, as at U, or an irregular 
mass of protoplasm, as at v, from either of which a new plant may spring, and in 
this habit’ the conidium agrees well with the resting-spore: the branch in this 
figure is shown as continuous, and though furnished with the vesicular swellings 
no partitions are present, the branches are frequently so seen. At w is illustrated 
a small weak plant, giving rise to a branch, which branch is developing into a large 
and strong plant ; such a phenomenon is by no means uncommon, and shows how 
the fungus increases itself in every possible way. I have frequently seen this 
secondary thread branched. 
During the last hours of completing this, the last engraving (fig. 4) illustra- 
tive of the Potato fungus, a new and curious fact came to light. On examining 
the oospores in saccharine fluid I observed some of the discharged bladders to be 
carrying from two to four secondary bladders inside (x); these secondary bodies 
were in their turn expelled, and grew and produced mycelium as at Y, Y, Y, whilst 
a few of the same secondary bladders burst and produced from three to six very 
small zoospores, generally only three. It is a most singular fact that these secon- 
dary bladders and zoospores are exactly the same in size with De Bary’s Pythium 
vexans, and about one-sixth or eighth of the bulk of the resting-spores from which 
they were discharged. With this exception there has not been the slightest 
approach in any of my material to organisms which might be referred to Pythium. 
Mr. Plowright writes : ‘‘ None of my oospores ever burst and produced Pythium 
or Pythium-like spores.” 
My material has contained a large number of dead mites and aphides and a 
few nematoid worms ; the oogonia and threads were to be seen in all parts of the 
dead insects, but not in the worms. 
De Bary, in reviewing my observation, says :—‘‘Even if the often men- 
tioned warty bodies were hibernating oospores of Phytophthora (Peronospora), 
like the similar oospores of P. Arenarize which resemble them, we shall not gain 
much information bearing upon these questions, since their ocurrence is, at the 
best, extraordinarily rare.” This sentence is very erroneous, for although the 
bodies were apparently rare when I first recorded their discovery, they were not 
necessarily so ina state of Nature, for on continuing the experiments after my 
first essay was written, the resting-spores were produced in myriads, and that, too, 
within the tissues of a comparatively few leaves. During the present spring I 
have sent mounted preparations of the mature (or almost mature) resting-spores to 
