GEORGE K. K. LINK 6oi 



The phenomenon of a transmissible lytic principle (bacteriophage) has been re- 

 ported by a few investigators as occurring in the plant field. This interesting but highly 

 controversial subject has however been merely touched, and more work will have to be 

 done before any definite conclusions can be drawn. Gerretsen and Sack, and Sohngen 

 and Gryns' report isolations of lytic principles from nodules, roots, and stems, but 

 not from leaves of leguminous plants bearing nodules, the lytic principles being specific 

 for the bacteria of the plants in question ; also from garden and field soil, but not from 

 heath or forest soil. Mallmann and Hemstreet^ report the recovery of an inhibitory 

 substance from cabbage decayed by fluorescent organisms, but did not demonstrate 

 lysis. Following their work, Coons and Kotila^ report recovery of a lytic principle 

 from rotted carrots, from soil, and from river water which in low dilutions inhibited 

 growth and in higher dilutions lysed B. carotovoriis, B. atrosepticus, and Bact. tume- 

 faciens. They report loss of motility, malformation, and agglutination as character- 

 istic of cultures treated with the lytic principle, agglutination being the first evidence 

 of change in the organisms. Kotila and Coons^ also report isolation of a lytic principle 

 from B. atrosepticus which when placed on potato tubers prevents the rotting normally 

 caused by this organism. They venture the suggestion that this principle is responsi- 

 ble for the rapid decline of B. atrosepticus in the soil. 



IMMUNOLOGY 



The field of phytobacteriology exhibits a wide range of problems in resistance- 

 susceptibility phenomena, practically all, or all, of which are instances of natural im- 

 munity. In the first place, it is an unanswered question why no or little success is had 

 in attempts of cross-inoculation of plants and animals with animal and plant patho- 

 gens. There are among plant pathogens a great number of instances of phylum, order, 

 family, genus, species, variety, and individual specificity. There are also illustrations 

 of tissue specificity so that bacterial diseases of plants are often contrasted as paren- 

 chyma and as vascular diseases. As a matter of fact, no sharp line exists and the dif- 

 ferences are largely quantitative rather than qualitative. Day^ however, reports that 

 Bact. salicis, the cause of the watermark disease of Salix caerulea, is strictly confined 

 to the vessels. 



There are abundant illustrations of susceptibility-resistance phenomena directly 

 correlated with age. In some diseases the seedling stage is the one during which the 

 plant is most subject to infection (wilt of maize caused by Aplanobacter stewarti), and 

 in many others tissues are susceptible only so long as they are immature (fire blight — 

 B. amylovorus). The correlation between immaturity and susceptibility makes many 



' Gerretsen, F. C, Gryns, A., Sack, J., and Sohngen, N. L.: "Das Vorkommen eines Bacterio- 

 phagen in den Wurzel-Knollchen der Leguminosen," Cenlralbl.f. BaklerioL, Abt. II, 60, 311-16. 1923. 



^Mallmann, W. L., and Hemstreet, C: "Isolation of an Inhibitory Substance from Plants," 

 J. Agr. Research, 28, 599-602. 1924. 



^ Coons, G. H., and Kotila, J. E.: "The Transmissible Lytic Principle (Bacteriophage) in Rela- 

 tion to Plant Pathogenes," Phytopath., 15, 357-70. 1925. 



•• Kotila, J. E., and Coons, G. H. : "Investigations on the Blackleg Disease of Potato," Michigan 

 Agr. Exper. Sta. Tech. Bull. 67. 1925. 



s Day, W. R.: "The Watermark Disease of the Cricket-Bat Willow {Salix caerulea)" Oxford 

 Forest. Mem., 3, 30. 1924. 



