184 Journal of Agricultural Research voi. vi, No. s 



EXPERIMENTAL METHODS 



As the methods for sterilizing, sampUng, and inoculating followed in 

 this study were similar to those outlined in a study of the brownrot 

 of the peach (7), they will be discussed here only briefly. The sterile 

 tubers were sliced longitudinally into four parts with a flamed knife. 

 Particular attention was given to obtaining portions of approximately 

 the same weight and same proportionate amount of cortex and pulp. 

 Each quarter was placed in a small wide-mouthed flask or large test 

 tube which had been stoppered with cotton, sterilized, and weighed. 

 The containers with the portions of potatoes were weighed again and 

 the samples were ready for inoculation. Two of the quarters from each 

 potato were inoculated from stock cultures of some one of the fungi 

 used in these experiments and a small quantity of sterile water was 

 added to each of the four containers. The four samples, two inoculated 

 and the two corresponding control samples, were placed side by side at 

 room temperature until the inoculated portions were well rotted. They 

 were then prepared and analyzed. The difference between the sound 

 and the rotted portions in the content of the compounds determined 

 was considered to be due to the action of the fungus. All control por- 

 tions infected at the time the samples were prepared for analysis and 

 all inoculated portions infected with organisms other than those used in 

 the inoculations were discarded. 



All samples were prepared for analysis by cutting them into very thin 

 slices with a sharp knife and washing them into the proper vessel. Pre- 

 cautions were observed, of course, that none of the juice or pulp should 

 be lost. The methods of analysis for agricultural chemists ^ were 

 usually followed in the determination of the various compounds. The 

 sugars were extracted from the tissue with alcohol and determined as 

 in the work on the brownrot of the peach. The method of extraction 

 is the alcohol method of Bryan, Given, and Straughn (3), somewhat 

 modified to suit the conditions of the experiment. The amount of cane 

 sugar was in all cases calculated from the reducing power of the extract 

 before and after inversion with acid. 



The starch determinations in the preliminary experiments were made 

 only by the direct acid-hydrolysis method using the finely ground potato 

 which- had been extracted with alcohol. In the work with the sound 

 and the rotted portions of the tubers, series of analyses were also made 

 by the diastase method with subsequent acid hydrolysis.^ Tollen's 

 phloroglucid method ^ was followed in all cases in the determination of 

 the pentosans. The methyl pentosans were determined according to 

 the method of Ellett and Tollens (6), by extracting the precipitated 

 phloroglucid with alcohol. The galactans and the crude fiber were de- 



• Wiley, H. W., ed. Official and provisional methods of analysis, Association of Official Agricultural 

 'Chemists. As compiled by the committee on revision of methods. U. S. Dept. Agr., Bur. Chem. Bui. 107 

 ■(rev.), 272 p., 13 fig. 1908. 



