644 



LABORATORY 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- 

 sylvania by inoculation of Pelargonium zonale with Pseudononas tumefaciens. (Photo 

 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 Dugg.^e, B. M.: Fungous Diseases of Plants, pp. 

 121-129. 



Lcttticc Drop {SdcTotinia Libertiana, Fuckel.).— Lettuce leaves may be in- 

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

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

 disease cmHrol, plants of lettuce should be kept for comparison (Dcggar, pp. 190-200) . 



Wilt of Sweet Corn {Bacterium (Pseiidomonas) Steu'arti E. F. Sm. (Fig. 229). — 

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



