Nov. is, 1920 Vascular Discoloration of Irish Potato Tubers 281 



18. Forty hill lots of the variety Rural New Yorker, grown on dis- 

 eased vines at Waupaca, Wis., in 1914. Cultural tests of the vines for 

 Fusarium at digging time yielded a Fusarium and a Colletrotrichum 

 culture in about equal numbers, but these did not appear to be general. 



19. Twenty-five hill lots of the variety Rural New Yorker, grown at 

 Greeley, Colo., in 1914 on vines infected with Fusarium oxysporum, as 

 shown by isolation tests from the vascular tissue of the stem9 at digging 

 time. 



PRESENTATION OF RESULTS 



VASCULAR DISCOLORATION 



The number of tubers in each lot of material and the number having 

 discolored vascular bundles, grouped according to the relative depth 

 of penetration below the stolon attachment, are shown in Table I. A 

 column for miscellaneous symptoms is included to provide for a variety 

 of incidental occurrences, such as net necrosis, decay, mechanical injury, 

 and the like; and following this, the number of tubers of each lot with 

 no vascular discoloration is shown. 



It has already been stated that, in general, tubers with stem-end 

 vascular tissue of normal appearance were not submitted to culture and 

 that one, two, or three cultures were made from tubers with discolored 

 vessels, the actual number being determined by the depth of the necrosis. 

 No regular procedure was adopted with respect to the tubers belonging 

 to the miscellaneous group. The figures in the column marked "theo- 

 retical," under "number of cultures," have been obtained by adding 

 the number of shallow discolorations, twice the number of deep discol- 

 orations, three times the number of very deep discolorations, and what- 

 ever number the notes show to be correct to provide the cultures made 

 from tubers with miscellaneous symptoms. The actual number of 

 cultures made and reported upon follows in the next column. Under 

 "duplicates" are included the number of cultures made from discol- 

 ored tubers in excess of the number theoretically required. The num- 

 ber of cultures made from tubers with no discoloration of the stem-end 

 tissue is next recorded, and last of all is given the number of cases in 

 which a culture was theoretically called for but was not reported. In 

 some cases, for one reason or another, these cultures were not made, 

 while in others they were made and discarded before being studied, 

 because of broken tubes, loss of identifying label, and similar accidents. 

 If the number given in the last column is subtracted from the sum of 

 the numbers in the two preceding columns and the difference is added to 

 the theoretical number of cultures, the actual number is obtained. 



