190 PerspecfJves in Microbiology 



that their distribution in plant tissues is sufficiently general 

 to provide immunity from destruction (46). 



The fundamental basis of resistance of plants to mi- 

 crobial attack is still to be disclosed. In the words of Coons 

 (6): "We do not know at all what makes one plant less 

 susceptible than another, nor do we know the basis of 

 fungus specificity that makes one species, genus, or family 

 of plants completely immune from a given parasite." This 

 might be generalized to include all kinds of microorgan- 

 isms as well as higher plants. The ability of plants to sur- 

 vive in contact with microorganisms, and of microorgan- 

 isms to develop in contact with one another, must depend 

 on compounds that prevent parasitic attack. Sherman and 

 Hodge (38) obtained a clue to the existence of such com- 

 pounds from the antibacterial action of expressed juices 

 of cabbage and turnip. Antimicrobial substances, desig- 

 nated "phytoncides," have been detected in many plants. 

 The fact that these substances do not seem to be present 

 in all plants, and that antibiotics are not presumed to pro- 

 vide protection to the cells that produce them, suggests 

 that the substances that provide resistance are unknown. 

 It remains to be established whether they are alike or dis- 

 similar in various plants and microorganisms, and whether 

 they are relatively stable compounds or must be continu- 

 ously regenerated or restored to an active state. The fact 

 that killed plants are very susceptible to microbial attack 

 tends to support the latter possibility. 



AnfibiofJcs and Plant Developmenf 



Before concluding my remarks, I should like to men- 

 tion briefly the relation of antibiotics and plant develop- 

 ment: that is, the production of antibiotics in soil and 

 their effects on the soil population, their uptake by plants, 

 their influences on plant development, and their use to 

 control plant diseases. 



