THE FUNGI WHICH CAUSE PLANT DISEASE 37 



those on which the galls have been found in nature, are susceptible 

 to artificial cross inoculation. Hard gall, hairy root, and soft gall 

 are also all due to infectious bacteria. 



As tentative hypotheses Smith assumes either: (1) That the 

 hairy root organism while resembhng the crown gall organism is 

 not identical with.it; or (2) That they are the same, and that if 

 infection takes place in a certain group of cells an ordinary gall 

 will develop, while if other special groups of cells are first invaded, 

 i. e., the root anlage, then a cluster of the fleshy roots will develop. 

 Some of his inoculation experiments point to the latter conclusion. 



Ps. vascularum (Cobb) E. F. Sm. ''"'• ^^' '" is parasitic on sugar 

 cane, filling the bundles with a yellow slime. It has not been re- 

 ported in America. 



Ps. sp. indet. A short rod, 2-i x 1-1.5 ju, actively motile by 

 1-3 polar flagella, was isolated from diseased spots on the larger 

 veins and petioles of beet leaves by Brown.™ The organism was 

 successfully inoculated in pure culture, disease produced, and the 

 organism reisolated. It is infective as well for lettuce, sweet 

 pepper, nasturtium, egg plant and bean. Agar colonies are creamy 

 white, thin, circular, turning the surrounding agar yellow-green 

 in three days. Gelatine is liquefied; litmus milk turns blue; 

 bouillon is clouded. Opt. 28°. 



Ps. sp. indet. A short rod, 2-4: n long, motile by 1-3 polar 

 flagella was isolated from diseased nasturtiums (Tropeolum) 

 leaves by Jamiesson.^ Pure culture inoculations induced typical 

 disease. The organism clouds bouillon; produces on agar small, 

 round, bluish-white colonies; liquefies gelatine and does not pro- 

 duce gas. Opt. 25°. T. D. P. 49-50°, 10 min. It is pathogenic 

 also for sweet-pea, lettuce, pepper, sugar-beet and bean. 



Bacillus Cohn. (p. 18.) 



This genus differs from Pseudomonas only in its peritrichiate, 

 not polar, flagella. Endospores are often present. Of the four 

 hundred and fifty or more species nineteen at least are known to 

 be plant pathogens. Numerous animal pathogens also belong to 

 this genus, notably B. typhosus, B. pestis. 



B. ampelopsorae Trev. is said to cause grape galls in Europe, 

 but the evidence is by no means conclusive. Cf. B. uvae. 



