LABORATORY AND TEACHING METHODS 



645 



quantities of a pure culture to a stem of young sweet corn and then pricking it in by 

 means of a sterile needle. Some have inoculated the young sweet corn plants 

 by placing the organism in the drops of water which exude from the tips of the corn 

 leaves early in the morning, but the inoculation by means of needle pricks is more 

 certain. Sections should be made of the stem at various stages of growth after 

 inoculation. This is done by using a number of plants. Free-hand sections, or 

 paraffin sections, will show the presence of the organism in the vascular bundles. 

 Stain with carbol fuchsin (Duggar, pp. 111-113). 



J^ 



W 



Fig. 228. — Arrangement of experiment for inoculation of pear twigs with blight 

 organism, Bacillus amylovorus. 



LESSON 31 



Black-rot of Cruciferous Planls {Bacterium (Pseudomonas) campesiris, Pammel) (see 

 Smith, Erw. F.: Bacteria in Relation to Plant Diseases, pp. 300-334; Duggar, 

 B. M.: pp. 107-111). — This organism is best inoculated into the stem of young 

 cabbage plants below the upper last three leaves, because of the tendency of these 

 leaves to drop off before the disease has progressed to its fullest extent. The stem 

 is first washed, the organism is smeared on at the point of inoculation and pricked 

 by a sterile cambric needle into place. It is recommended that several sections 

 be made, and that to secure the several stages, a number of different inoculations 

 be made. 



