or by some bacteriologist, using pure cultures and plant juices which have been sterilized by filtration.

Dr. Russell's experiments were made a year earlier than than those of Wiesner and have the merit of being properly performed, i. e. with sterile juices and pure cultures so that the conditions under which the experiments were made can be reproduced by other investigators. They are, however, too limited in number to afford any basis for a general conclusion. He found that Canna juice, sterilized by filtration, exerted no appreciable germicidal effect on any of the following species: Kiel-water bacillus, B. lactis-ærogenes, B. coli-communis, B. megaterium, B. prodigiosus. Experiments with B. megaterium, B. butyricus, B. coli-communis, B. pyocyaneus, and Streptococcus pyogenes, using as a culture medium root-pressure juice obtained under sterile conditions from the severed stem of lima beans and Pelargoniums led to a similar conclusion and to the enunciation of the following general statement: "vegetable cell juices, aside from their acid reaction, are entirely powerless against bacteria, and do not possess any germicidal properties like the blood serum of animals."

The old view that plants are not subject to the attacks of bacteria simply because their tissues are acid was shaken by the discovery that some bacteria grow very well in acid media, and was thoroughly upset by the discovery that the juices of some parts of many plants are alkaline. In all probability plants like animals require a delicate balance between acid and alkaline and a continual change from one side to the other for the carrying on of the life processes. Three things at least are certain (1) It will not do to assume that all parts of a plant are acid because some part of the parenchyma shows a strongly acid reaction; (2) It cannot be stated that any given microorganism will thrive only in alkaline media until this fact has been determined by direct experiment; and (3) Many bacteria, perhaps all, are alkali producers and capable, if they can gain any foothold whatever, of slowly changing an unsuitable acid medium into one more alkaline and better adapted to their use.

"Russell: (9) Bacteria in their Relation to Vegetable Tissue. Thesis. Johns Hopkins University. 1892, 8vo. p. 41.

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Wiesner's hypothesis is somewhat different. It has been known for some time that various essential oils and other vegetable products, e. g. thymol, salicylic acid, benzoic acid, tannin, quinine, oil of cinnamon, oil of peppermint, etc., exert a powerful restraining influence on the growth of many bacteria, and it is not improbable that a great variety of bactericidal and protective substances occur in plants. On the other hand there may be and probably are bacterial parasites capable of thriving in the very plants which Wiesner found most resistent to continuous spray, to the saprophytic bacteria of stagnant water, and to those of decaying meat infusions, the exact conditions under which any given microorganism will thrive being determinable only by experiment. It must also be remembered that the physiological requirements of bacteria often become profoundly modified to suit changed environments, and that all parasites have undoubtedly descended from saprophytic forms. Prof. Wiesner has, however, opened up a very inviting field and its further investigation by some careful experimenter, trained in bacteriological methods, might lead to very interesting discoveries.

Most of the recent books on vegetable pathology devote a chapter to the bacterial diseases of plants, but these books have not been written by bacteriologists and consequently the statements given are usually very meager and unsatisfactory, and forcibly illustrate the fact that no one can write acceptably on a subject with which he is not familiar, not even if he possesses a logical mind and has read all the "authorities." Excepting Prof. W. Migula, who reviewed the subject briefly but somewhat carefully in 1892, and Dr. H. L. Russell, who gave a brief summary in tabular form the same year at the end of his Thesis," no one seems to have gone over the field critically since de Bary's time, although there is now a considerable body of literature. It is proposed, therefore, in the following pages to examine the literature of this subject from the standpoint of the

10

10 Migula (10) Kritische Uebersicht derjenigen Planzenkrankheiten, welche angeblich durch Baktrien verursacht werden. Semarang. Midden-Java. 1892. Exp. Sta.

11 Russel: 1. c., pp. 36-41.

modern bacteriologist, sifting as far as possible the wheat from the chaff, and arranging all in an orderly way for convenient reference. The utility of such a piece of work, if well done, can scarcely be questioned, since it must set into sharp relief the gaps in our knowledge and tend to stimulate further research. The work of the early investigators already mentioned was done before the perfection of modern methods of bacteriological research, and in a time of general scepticism which some of us well remember. It is therefore in no way discreditable that many of their conclusions should be found untenable when tested by the more rigid requirements of the science of to-day. They worked under great difficulties and did as well as could be expected even of men of genius, better, indeed, than many of us would have done. Certainly, as pioneers in a difficult field they deserve great credit.

As much cannot be said for some of the more recent workers who with every opportunity in the way of literature, including numerous manuals of bacteriology, and with laboratory facilities for learning the fundamentals of bacteriological research on every hand in every land, have been content to publish second and third class work, exactly like that preceeding the discoveries of Pasteur and Koch and the development of modern methods. One might suppose these people to have been in a deep sleep for the last twenty years, they take so little note of what has been going on. I shall have frequent occasion to consider papers of this class in the course of these pages and shall not fail to point out their worthlessness, to discourage imitators, if for no other reason. It goes without saying that such publications do not advance science, nor in the end in any way contribute to the reputation of the individual. They are thoroughly discreditable, and in case new species are erected, are little less than criminal, considering the present overburdened and chaotic state of systematic bacteriology.

Thanks to the itch for species making, systematic mycology is generally cited as the most desperately confused and perplexing branch of natural science, but mycology is a highway turnpiked and provided with arc lights in comparison with the wilderness of systematic bacteriology. Of the thousand or

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more forms which have been studied and named, or designated by letters or figures or vernacular names, probably not one-tenth can be identified with any certainty owing to the meagerness of the descriptions. The older descriptions are particularly bad, and the effort to decide what was meant by these old names, for which somebody will by and by be strenuously claiming inalienable rights of priority, is usually time. thrown away. There is quite enough to do in bacteriology, as every one knows who is dealing at first hand with its hard problems, without wasting precious energy in striving to guess what was meant by two and three line descriptions. All descriptions which do not describe, and there are many such, ought to be wholly ignored, and no species recognized as worthy of a place in literature unless so characterized as to be identifiable by others. A plea of this sort in the higher branches of botany or zoology would be a subject for laughter. Bad descriptions are however, so much the rule in bacteriology that it is no laughing matter but rather a great evil urgently demanding reform. It is a state of affairs which has come about naturally enough considering the way in which bacteriology has developed13 but which would not now be tolerated for a moment in phanerogamic botany or in most branches of zoology and the continuance of which in bacteriology it is incumbent on every honest worker to limit and discourage in all possible ways. The best way in science, always, is to speak out plainly, and to join hands for the advancement of a good cause. Bad work should be ignored and "new species" relegated to limbo unless the descriptions conform to the requirements of modern bacteriological science, meaning by this expression the consensus of opinion among experienced and careful investigators everywhere. If there were some such agreement among the better class of workers, the improvement in systematic bacteriology would become very marked. The volume of publication would, indeed, decrease noticeably but this of itself

12 About 650 species are mentioned in (11) Schizomycetaceæ, by de Toni and Trevisan in Saccardo's, Sylloge Fungorum, VIII, published in 1889, but this is not complete.

13 All the early systematists built upon a foundation of sand, i. e. upon pure morphology.

would be a great advantage, and the quality of the work would more than correspondingly improve. Only in some such way can the strong tendency toward trashy publication be eliminated and light and order evolved from the present chaos.

With few exceptions, vegetable pathology seems to have been specially unfortunate in the class of persons who have devoted themselves to the study of bacterial diseases. While the bacterial side of animal pathology has had its Pasteur and Koch, its Esmarch, Hueppe, Flügge, Gaffky, Frænkel, Pfeiffer, Loeffler, Duclaux, Metchnikoff, Chamberland, Roux, Welch, Sternberg, Smith, Prudden, and a host of other skilled experimenters, scarcely less eminent, and has made correspondingly great progress, the study of the bacterial diseases of plants has been principally in the hands of botanists without special laboratory training in bacteriology and even destitute in some cases of an elementary knowledge of right methods of work. The great development of modern bacteriology is attributable largely to the discovery that human diseases are due to these organisms, and to its consequent alliance with medicine, but there is no reason why the same rigid scrutiny of methods and sharp calling in question of statements which have led to such brilliant results in animal pathology in recent years should not be applied in the same way to vegetable pathology. Accurate experimentation and trustworthy results are from a purely scientific standpoint quite as desirable in one field as in the other.

Two things are especially to be kept in mind in describing any bacterial disease of plants: (1) The pathogenesis must be worked out conclusively; (2) If the organism is named, it must be so described that it can be identified by any competent bacteriologist no matter where it is found.

The four requirements under the first head, i. e. Pathogenesis, are now generally recognized to be as follows:

A. Constant association of the germ with the disease.

B. Isolation of the germ from the diseased tissues and study of the same in pure cultures on various media.

C. Production of the characteristic symptoms of the disease by inoculations from pure cultures.