TRANSACTIONS OF SECTION K. 1047 



Si/mptoms. — The shoots turn yellow and die prematurely during the summer, 

 and before the tubers are anything like full. The disease xtarin from Mow and 

 not from the leaves. The roots are few and poor, and soon rot away. The tubers 

 are few, do not mature, and often rot in the ground. The leaves turn yellow and 

 wither on the stems, with the symptoms of premature wiltint/, and often remain 

 long hanging on the yellowing, glassy-looking, but still living stems. 



In very mild cases these symptoms are not obvious, and supervene slowly, and 

 the case may be complicated by the co-existence of Phi/tophthora. 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 hyphae. 

 In several cases I have traced these hyphie through every internode of the stem, 

 into the petioles of the still hanging leaves, into the young lateral shoots, through- 

 out the roots and subterranean rhizomes, and up to and even jvjst 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. Tyloses 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 con- 

 siderable resistance to the invasion of the fungus; but 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 micro&copic 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 yathered aud stored dry. 



But if wet, various kinds of rot may supervene, owing to the subsequent invasion 

 of various micrococci, bacteria, fungi, &c. following 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. 



The principal point is that the fungus I have especially studied leads the way 

 for these purely saprophytic anaerobic and aerobic forms into the tuber : once in 

 the mature tuber, its progress is necessarily slow until the reserves move in the 

 spring. 



During tlie past winter I gave to Miss Dawson, who is working at such sub- 

 jects in my laboratory, some of the tubers saved from plants attacked with this 

 disease, to investigate the various fungal forms lurking in the diseased tubers. 

 Her investigations are not yet completed, but enough has been accomplished to 

 convince us that after the fungus in question has opened up the way into the 

 tuber, all sorts of bacteria and fungi can make their way down the destroyed 

 vascular strands, aud reappear in spring, when the tubers are replanted. 



But this is not all. The evidence shows that the fungus in question, once in 

 the tuber, leads a dormant life during the early part of the winter, but gradually 

 invades the new sprouts as they slowly appear in the early spring, aud that the 

 parasite is actually replanted by the farmer or gardener, when restocking the 

 ground, in his neio ' sets.^ 



If we reflect that the tuber is really a bud, there is nothing especially strange 

 in this phenomenon ; the fungus enters the base of the bud in autumn, and takes 



