attitude; op pathologists and BACTgRIOI^OGISTS. 15 



The ^English edition of von Tubeuf (1897) does not differ essentially from the German. 



Frank's Kampfbuch, published in 1897, is chiefly interesting in this connection, because 

 in it the author announces his changed views respecting the existence of bacterial diseases 

 of plants. Concerning them we have the following very cautious recantation (p. 201) : 



Whether bacteria can be the cause of disease in plants is always a question to be considered 

 with circumspection. In case of the potato-rot this doubt was formerly so much the more justified 

 because we had learned to know a genuine thread-fungus, the Phytophikora, as the cause of this 

 disease, and consequently the suspicion at once arose that perhaps this fungus was really the true 

 cause of the disease and might have paved the way for the entrance into the potato of the decay 

 bacteria. I myself have held fast to this doubt until quite recently, but must give it up as a result 

 of my own investigations recently instituted. 



In his Vorlesungen, published in 1897, Fischer takes the ground that there are no 

 bacterial diseases of plants and can not be any for reasons cited, to wit, the bacteria can 

 not enter the plant except through wounds, and their development in the latter is soon 

 stopped by the formation under them of an excluding layer of cork. Stomatal infection 

 is altogether impossible for the reasons stated : 



Die unverleizte Pflanze steht mit der Aussenwelt nur durch die Spaltoffnungen in offener Ver- 

 bindung, die selbst sich darauf beschrankt, dass das gegen die Zellen ganz abgeschlossene System 

 der lufterfiillten Intercellularraume mit der Aussenluft kommuniziert. Wenn durch den Wind oder 

 durch Regen Bakterienkeime in die Spaltoffnungen gefuhrt werden, so gelangen sie von hier aus nur 

 in diese Intercellularraume, wo ihnen ausser dampfgesattigter Luft nichts weiter geboten wird, wo 

 alle Nahrstoffe fehlen, ohne die keine Bakterienspore auskeimt, keine Bakterienzelle sich vermehrt. 

 * * * Alle diese Fahigkeiten fehlen den Bakterien, gegen die eine unverletzte Pflanze vollkom- 

 men geschiitzt ist. Aber auch die verwundete Pflanze wiirde nur in den geoffneten, verletzten Zellen 

 Nahrstoffe fiir Bakterien darbieten, eine Quelle, die bald dadurch abgeschnitten wird, dass unter 

 der Wundflache eine undurchlassige Korkschicht (Wundkork) entsteht, die jeden weitern Safteaus- 

 tritt aus der Wunde verhindert. Die Wunde bleibt nicht feucht, die verletzten Zellen schrumpfen 

 und trocknen ein und damit ist den Bakterien der Eingang genau so versperrt, wie an der unver- 

 letzten Pflanze. Ihr drohen demnach auch keine Wundinfektionskrankheiten durch Bakterien, deren 

 Weiterverschleppung in der Pflanze gleichfalls unmoglich ist. 



The following is a translation of the entire paragraph : 



Exclusive of the tubercle bacteria whose wonderful relation to the Leguminosae has been 

 described already (Vorl. X), no single example is yet known of bacteria which can insinuate them- 

 selves into the closed Hving cells of a plant. The uninjured plant stands in open connection with 

 the outer world only through the stomata, which connection is so limited that the system of air 

 filled intercellular spaces connects with the outer world but is entirely closed to the cells. When 

 bacterial germs are forced into the stomata by wind or rain, they here reach only into these inter- 

 cellular spaces where nothing further is offered to them than vapor-saturated air, where all nutrient 

 substances are wanting, without which no bacterial spore can germinate, no bacterial cell can 

 multiply. Even when such bacteria as can dissolve cellulose (the methane bacteria) are brought 

 into the intercellular spaces they can not noiuish themselves here, and can not develop their pecu- 

 liarity of dissolving the cell-wall. Consequently only those parasitic organisms can penetrate into 

 the plant with results, whose spores have brought along with them sufficient nutrient substance so 

 that they can germinate in pure water, so that they can overcome the lack of nutrient substances 

 which they meet with at first, and can open their attack on the protective cell-wall at their own 

 expense. This requirement is fulfilled by the spores of parasitic fungi, which with their reserve 

 stuff push out a germ-tube, which now bores directly through the epidermis of the plant (potato 

 fungus, Phyiophthora infestans) or which first penetrates into the intercellular system through a 

 stoma (rust fungi), and from here boring through the cell-wall, multiplies in the cells, or at least 

 sends into them special side branches of its myceUum as sucking organs (haustoria). AU these 

 peculiarities are wanting in the bacteria, against which an uninjured plant is fully protected. But 

 also the wounded plant offers food for bacteria only in the opened, injured cells, a soiurce which is 

 soon removed by the formation under the wounded surface of an impenetrable cork layer (wound 

 cork) which entirely prevents any further flow of sap from the wound. The wound does not remain 

 moist, the injured cells shrivel and dry out, and consequently the entrance of the bacteria is exactly 

 so barred out as in the uninjured plant. Consequently, there is not the least danger of wound- 



