Pe'I'HYBRIDGk and Murphy — Bacterial Disease of the Potato. 5 



hy any means sufficient to judge of the identity of diseases in plants when 

 bacteria are concerned ; and in the absence of cultural experiments, there is no 

 proof that the Irish plants were really attacked by B. solanincola. Delacroix 

 in this paper identifies much of what is known in France as " brunissure " 

 (browning) of the potato as being caused by the attacks of the above organism. 

 The disease does not show itself as a rule earlier than the second fortnight in 

 the month of July. The shoots of the plants cease to develop, the leaves 

 yellow and become of a greyish fawn colour, and then dry up. The base of 

 the stem often shows on its surface livid spots, and, in cross-section, transparent 

 brown patches reaching more or less high up the stem. The underground 

 parts often show wounds which may or may not be healed. It is through 

 these, Delacroix considers, that the potato plant becomes attacked. For, 

 while not denying that the disease may be spread by means of affected tubers 

 which give rise to diseased plants, he believes that the chief source of attack 

 is from the soil, B. solanincola being regarded as being essentially a soil- 

 organism. The tubers may also be affected, becoming brown, starting from 

 the " heel " end. As mentioned before, the production of gum and thy loses in 

 the wood vessels of the stem is a well-marked character. The organism 

 usually exists as single individuals, and is rarely found in pairs, and never as 

 a zoogloea. It is scarcely motile, bears no fiagella, and does not produce 

 spores. It is quite clear, therefore, that Delacroix had before him a well- 

 marked disease of the potato caused by the definite organism B. solanincola. 

 It seems certain that a somewhat similar disease existed at the time in 

 Ireland. Johnson (21), in 1902, refers to his communications with Delacroix, 

 and states that his first specimens were thought by the French observer to be 

 attacked by Bacillus caulivorus. Specimens, however, seen a couple of years 

 later, were put down as being attacked by Bacillus solanincola. Judging from 

 cultures he had made, Johnson states that he concludes that B. caulivorus, 

 B. solanincola, and B. solanacearuyn, are all present as disease-producers iu the 

 potato in Ireland. That all these organisms pathogenic to the potato should 

 be found carrying on their destructive work in Ireland seems, judging from 

 analogy with other countries, at least highly improbable; and up to the 

 present at least no really clear evidence on the matter has been published. 



In the course of the study of the bacterial diseases of a variety of plants, 

 van Hall (16), in the year 1902, described, under the name of " Zwartbeenigkeid," 

 a bacterial disease of the potato in Holland, which he had observed for the 

 first time during the previous summer. The disease shows much the same 

 characteristics as the " Schwarzbeinigkeit " of German authors, and the Black 

 Stalk-rot which we are about to describe. An organism was isolated which 

 proved highly toxic to the potato-plant, and less so to other plants. It 



