48 
slowly, and the case may be complicated by the co-existence of 
Phytophthora. In very severe cases, on the other hand, especially in 
wet situations, the stems and roots may be all rotten by the end of 
July, and casual observation may ascribe the damage to Phytophthora 
entirely. In ordinary cases, again, it is easy to suppose the damage 
due to some insect attack, or to drought. 
In advanced stages of the disease the stems either dry up to brown 
sticks, or putrefy on the wet ground; very often bacteria have 
gained access to the tissues at a comparatively early stage. 
Microscopic Appearances.—Sections across the lower parts of the 
attacked stems show one, two, or more of the vascular bundles: 
yellowish-brown—visible even without a lens—and the principal 
vessels of these contain branched, septate hyphz. In several cases 
I have traced these hyphz through every internode of the stem, into 
the petioles of the still hanging leaves, into the young lateral shoots, 
throughout the roots and subterranean rhizomes, and up to and 
even just into the tubers. In two cases I have done this in one 
and the same potato-plant, and so have no longer any hesitation 
in ascribing the disease to this fungus, the morphological features 
of which will be described in a subsequent paper. In advanced 
cases the brown vessels are stopped with a yellowish gum-like 
substance. Iyloses are common in the vessels of the root. Those 
tubers which are not attacked while still very young, but which 
have already begun to fill with starch, may offer considerable 
resistance to the invasion of the fungus ; bnt eventually the vascular 
strands diverging from the point of attachment to the rhizome 
exhibit the tell-tale foxy-red or yellowish-brown colour, and in 
many cases the ripened tubers are to all appearance sound, except 
for microscopic reddish spots just at the points of entry of these bundles. — 
During the winter the stored potatoes, with the fungus thus just 
lurking in them at the morphological base (the so-called heel) of the 
tuber, may undergo little change to all appearance if gathered and 
stored dry. 
But, if wet, various kinds of rot may supervene, owing to the 
subsequent invasion of various micrococci, bacteria, fungi, &c., follow- 
ing the lines of weakness opened up by the fungus in question, and 
living as saprophytes on the stored reserves. 
In some cases even apparently dry tubers may undergo a curious 
rot—dry-rot—owing to the ravages of a particular bacterium or mould, 
perhaps more than one, which finds sufficient moisture for its 
purposes, : 
