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sarc secretes some zymogen which perfects the digestive secretion.

The object to which the acid would seemingly serve in these organisms, which may be said to be on the very threshhold of life is the same which Bunge ascribes to it in man. Bunge's view is that the HCl has no other purpose than the sterilization of food.

Why should a chemical substance be placed in the entrance to the digestive tract,” he asks,“ in exactly the strength necessary for the destruction of bacteria which is directly antagonistic to the chemical reaction in which the main work of digestion must be carried on? The proteids are more readily converted into a solution lower down in the intestine and in an alkaline medium than by pepsin and acid. The object of the acid is, according to him, then, one of sterilization. This view cannot be denied, at the same time it must be admitted that HCl serves also a digestive purpose.

In the Rhizopods experimented upon, the observations of Greenwood and Saunders could be confirmed concerning the fact that while the acid is secreted in the food vacuoles under the stimulus of all ingesta ; the true digestive vacuole which occurs only under the stimulus of nutritive matter apparently contains something besides an acid, perhaps an enzyme. The change in the acid indicators is as regards time and intensity of color transformation to all observation alike. There seems to be the same amount of acid in a storage vacuole as in a vacuole causing active solution of proteid matter, in close proximity to it, hence the assumption of an additional zymogenic substance in the latter is justifiable. As the amount of acid in one of these vacuoles is very small, and the change in Congo red to blue is speedy and striking, lends belief to the suggestion of Greenwood that the acid is an inorganic one. Why the protoplasm around a storage vacuole will not secrete zymogenic matter, though acid is clearly present in it, and at the same time this enzyme must be accepted to be present in a vacuole in which, close to the former, active digestion is going on is a question difficult to approach. If it can be demonstrated that all or most storage vacuoles contain some substance, living or inert, which is hostile to the economy of the Rhizopod and against which it protects itself by intensely acid

investment of the enemy for a prolonged period, a new and interesting light will be thrown on this phenomenon.

In the “Centralblatt für Bacteriologie, Parasitenkunde u. Infektions krankheiten, Vol. XIX, p. 785, Dr. C. Gorini describes a method for cultivating Amoeba zymophila on a solid medium which in this case is the potato. It is certain that Amoebae will grow on old and new potatoes with alkalinization. This would offer an easy and convenient method of cultivating them. It should be emphasized that it is almost impossible to produce cultures of amoeba that are absolutely free from bacteria. A. Celli in the Centralbl. f. Bacteriologie, Bd. XIX, p. 537, describes a number of futile attempts to obtain such cultures. For our purpose it is not essential that the amoebic cultures should be absolutely free from bacteria, a relative, approximate sterility is sufficient to demonstrate the scarcity of storage vacuoles in the amoebae and plasmodia in such environment. Celli's favorite solid medium is a preparation made from Fucus Crispus with 5 per cent Sterilized Water, with or without Bouillon, but always made alkaline. To 10 c.c. culture medium, 1 c. c. of an N Solution of Potassium hydroxide or 4-5 c. c. of a saturated solution of Sodium Bicarbonate. This culture medium of Fucus after it is made in the manner that Agar is generally prepared solidifies readily.

In the same Journal, Centrbl. für Bacteriologie, Band XIX, p. 258, Dr. M. W. Beyerinck describes a solid medium for amoebic cultures made from solidified agar by diffusion of the soluble organic substances in it into superimposed distilled water, which process requires about two weeks and repeated sterilization and subsequent addition of salts suitable to formation of nitrites.

I have no experience with these methods and have always found that for my purpose a solution of a little wheat bread in distilled water kept in a small flat dish under a glass cover was all that was required to have Amoeba and plasmodia of mycetozoa constantly on hand. The dish must be kept on a little earth and not in too bright a light and at a constant temperature. This simple culture medium, which of course is unsuitable for pure cultures was suggested by Prof. Reichert of the University of Pennsylvania.

THE BACTERIAL DISEASES OF PLANTS:.

A CRITICAL REVIEW OF THE PRESENT STATE OF

OUR KNOWLEDGE.

By ERWIN F. SMITH.

I.

It is scarcely fourteen years since Dr. Robert Hartig declared that there were no diseases of plants due to bacteria. Two years later Dr. Anton de Bary, unquestionably one of the most learned and critical botanists the world has ever known and the foremost student of cryptogamic plants, expressed the belief that bacterial diseases of plants were of rare occurrence, and suggested as a partial explanation the fact that the tissues of plants generally have an acid reaction.” In his Vorlesungen über Bacterien, published in 1885, he expresses much the same opinion, and cites only four diseases, viz., Wakker's hyacinth disease, Burrill's pear blight, Prillieux's rose red disease of wheat grains, and the wet rot of potatoes, described by Reinke and Berthold. Concerning the first of these four diseases he says: “Successful infection experiments and exact study of the life history of the bacterium are still wanting.” Respecting the second he contents himself with briefly summarizing the statements made by Prof. Burrill. Of Prillieux's micrococcus he says: “Its importance as a cause of disease cannot be determined with any certainty from the brief account. It may turn out to be only secondary, appearing as a saprophyte in consequence of injuries previously received.” Concerning the wet rot of potatoes he states that ordinarily it is a secondary phenomenon following the attacks of the parasitic fungus Phytophthora infestans, but admits that exceptionally potato tubers may become wet rotten without the presence of Phytophthora, and that "the above named observers succeeded in producing the appearance of wet rot in sound potato tubers by inoculations with their bacteria ; in agreement with which stands a recent experiment of van Tieghem, who succeeded in totally destroying living potato tubers by means of Bacillus amylobacter when he introduced this into the interior of the tuber and maintained the same at a high temperature (35°)."

1“ Für die Krankheitsprocesse der Pflanzen kommen sie durchaus nicht in Frage, etc.” Hartig : (1) Lehrbuch der Baumkrankheiten, 1882, p. 27.

2. Bacteria parasitic on plants have scarcely ever been observed, a fact to which R. Hartig has already drawn attention. One reason for this may be that the parts of plants have usually an acid reaction.” De Bary: (2) l'ergleichende Morphologie und Biologie der Pilze Mycetozen und Bacterien, 1884, p. 520; English ed., p. 481.

3“ According to the present state of our knowledge parasitic bacteria are of but little importance as the contagia of plant diseases. Most of the contagia of the numerous infectious diseases of plants belong to other animal and plant groups, principally, as already noted, to the true fungi.” De Bary: (3) Vorlesungen ueber Bacterien, 1885, p. 136.

In the second edition of his Lehrbuch, published in 1889, Dr. Hartig modified his statements somewhat, expressing essentially the same opinions as de Bary. The yellow rot of hyacinths is recognized as a bacterial disease, although rather doubtfully in as much as it is said not to attack sound, well-ripened bulbs, under normal conditions, but only when they have received wounds or been attacked by fungi, especially by a hyphomycete which is said to be an almost constant accompaniment of the rot. The wet rot of potato tubers is admitted to the list, but with the statement that it is mostly a secondary matter, following the rot of stem and cells due to Phytophthora infestans. One other bacterial disease is mentioned, viz., pear and apple blight, with the suggestion, however, that it may have been erroneously attributed to bacteria, since the fungus Nectria ditissima produces in the bark numerous little bacterialike gonidia.

Such was the general opinion on this subject down to within less than a decade. Even today the majority of well educated botanists would find nothing to contradict in the statement that there are very few diseases of plants distinctly attributable to bacteria. As a matter of fact, however, there are in all probability as many bacterial diseases of plants as of animals.

Various explanations have been advanced to account for this freedom or supposed freedom of plants from bacterial parasitism. As we have already seen, de Bary was inclined to ascribe it in good part to the acid reaction of vegetable tissue. Dr. Hartig's view is best expressed in his own words: “Whereas the processes of decay, and most of the infectious diseases of man and animals, may be traced to bacteria, the plant organ: ism is protected against them by the peculiarity of its structure, and especially by the absence of circulatory channels for con. ducting the nutrient fluids which could serve to distribute any lowly organisms which might happen to be present in the food. It is only by means of the vessels and intercellular spaces that they can distribute themselves in any great numbers in the body of the plant, for in other cases they have to pass through the cellulose or woody cell walls, which offer great resistance to their attack. In addition to this, the vegetable juices, most of which show an acid reaction, are unfavorable to their growth. As a matter of fact, bacteria have hitherto been found only in the tissues of plants whose cells are parenchymatous in character and possessed of very delicate walls, as for instance, bulbs and tubers."

For several years Ph. van Tieghem experimented with one or more, probably several, bacteria, called by him Bacillus Amylobacter and believed to be the specific agent in the decomposition of cellulose. In 1879," he stated that all the cells of all plants are equally dissolved by it in the meristematic stage but that as soon as the tissues have become differentiated profound differences are noticeable. The cellulose of many plants is dissolved by it but that of mosses, sphagnums, hepatics, lycopods, fern leaves, and stems and leaves of phanerogamous aquatics proved resistant. This behaviour of water plants is "une nécessité d'existence." In 1884, he made a number of additional similar statements. The tubers of the potato, the seeds of beans (first swelled in water and then inoculated directly into the substance of the cotyledons), and the fruits of cucumbers and melons rotted quickly when infected with this organism. Inoculated leaves of Crassulaceæ and stems of Cac

* Hartig: Lehrbuch. 2nd. Edition. English translation, p. 37.

6 Van Tieghem : (+) Sur la Fermentation de la Cellulose. Bull. de la Soc. Bot. de France, 1879, pp. 25 to 30.

• Van Tieghem: (5) Développement de l'Amylobacter dans les plantes à l'état de vie normale. Ibid., 1884, pp. 283–287.

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