Fungi, Bacteria und Pathologie. 675 



Massee, George, On the origin of parasitism in Fungi. 

 (Philosophical Transactions of the Royal Society London. 

 Series B. Vol. CXCVII. 1904. p. 7—24.) 



The author's abstract is as follows. 



Up to the present no definite explanation has been ofiered as to 

 why a given parasitic fungus is often only capable of infecting one par- 

 ticular species of plant. This, however, is well known to be the case, 

 for although the spores of fungus parasites germinate freely on the sur- 

 face of any plant when moist, infection only takes place when the spores 

 germinate on the particular species of plant on which the fungus is 

 known to be parasitic. This apparently selective power on the part of the 

 fungus the author considers to be due to Chemotaxis. 



An extensive series of experiments were conducted with various 

 species of fungi, including saprophytes, facultative parasites, and obli- 

 gate parasites, and the results are given in tabulated form in the füll 

 paper. The chemotactic properties of substances occurring normally in 

 cell-sap were alone tested; among such may be enumerated Saccharose, 

 glucose, asparagin, malic acid, oxalic acid and pectose. In those in- 

 stances where the specific substance, or combination of substances, in 

 the cell-sap assumed to be chemotactic could not be procured, the ex- 

 pressed juice of the plant was used. 



These experiments proved that saprophytes and facultative para- 

 sites are positively chemotactic to Saccharose, and this substance alone 

 is sufficient in most instances to enable the germ-tubes of facultative 

 parasites to penetrate the tissues of a plant, unless prevented by the 

 presence of a more potent negatively chemotactic or repellent substance 

 in the cell-sap. 



As an Illustration. Botrytis cinerea, which attacks a greater number 

 of different plants than any other known parasite, cannot infect apples, 

 although Saccharose is present, on account of the presence of malic acid, 

 which is negatively chemotactic to the germ-tubes of Botrytis. 



In the case of obligate parasites the cell sap of the host-plant pro- 

 ved to be the most marked positive chemotactive agent. ' Malic acid is 

 the specific substance that attracts the germ tubes of Monilia fructigena 

 into the tissues of young apples; whereas enzyme pectase performs the 

 same function for the germ-tubes of Cercospora cucumis, an obligate 

 parasite on the cucumber. 



Immune specimens of plants belonging to species that are attacked 

 by some obligate parasite owe their immunity to the absence of the sub- 

 stance chemotactic to the parasite. 



Purely saprophytic fungi can be educated to become parasitic, by 

 sowing the spores on living leaves that have been injected with a sub- 

 stance positively chemotactic to the germ-tubes of the fungus experi- 

 mented with. By a similar method of procedure, a parasitic fungus can 

 be induced to attack a different species of host-plant. 



These experiments prove what has previously only been assumed, 

 namely, that parasitism in fungi is an acquired habit. 



A series of experiments prove that infection of plants by fungi 

 occurs more especially during the night, or in dull damp weather. This 

 is due to the greater turgidity of the cells, and also to the presence of a 

 larger amount of sugar and öther chemotactic substances present in the 

 cell-sap under those conditions. A. D. Cotton. 



Saccardo, P. A., C. H. Peck and William Trelease, The Fungi 

 oi Alaska. (Forming pages 13 to 53 of the Harriman 

 Alaska Expedition. Vol. V. Issued April 2, 1904.) 



The present paper on the fungi of Alaska is the list of the fungi 

 collected by the members of the Harriman Alaska Expedition. The 

 determinations of the various types were made largely by the authors 

 as given above, and after a brief introduction by William Trelease, 



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