644 



LABORATOEY EXERCISES 



For this and other experiments consult Melhus, T. E.: Culture of Parasitic 

 Fungi on Living Hosts. Phytopathology, ii: 197-203, October, 1912. 



Pear Blight (Bacillus amylovoriis, Burrill) (Fig. 228). — Take some pear twigs 

 long enough to be accommodated easily under an ordinary bell jar. Cut off 

 these stems under water and transfer to a jar under water, so that the cut ends are 

 not exposed to the air. Then make slanting cuts at the upper end of the twigs 

 with a sterile knife and inoculate the cut ends with the organism. Cover the twigs 

 and jar in which they are placed with a bell jar, as shown in the accompanying 



Fig. 



227. — Crown gall artificially produced in greenhouse of University of Penn- 

 by inoculation of Pelargonium zonule with Pseudononas tumefaciens. {Photo 



syl 



by Charles S. Palmer.) 



illustration. Note the result of the inoculation on the tissue of the twigs and on the 

 health of the leaves. Consult Duggar, B. M.: Fungous Diseases of Plants, pp. 

 121-129. 



Lettuce Drop (Sclerotinia Libertiana, Fuckel.).— Lettuce leaves may be in- 

 oculated by means of the sclerotia of fungus,' or by the mycelium laid upon the sur- 

 face of scarified areas of the leaf. As inoculation produces a virulent form of the 

 disease control, plantsof lettuce should be kept for comparison (Duggar, pp. 190-200). 



Wilt of Sweet Corn {Bacterium {Pseudomonas) Stewarti E. F. Sm. (Fig. 229). — • 

 This organism was furnished on beef agar and is best inoculated by applying small 



