822 
Journal of Agricultural Research 
Vol. XXI, No. It 
TRANSMISSION OF ORGANISMS IN SEED POTATOES 
materials and methods 
In 1916 several lots of diseased and healthy potatoes of different 
varieties and from several localities were secured as follows: Seven 
lots of diseased potatoes—one each of American Wonder, Burbank, 
Early Rose, Up-to-Date, and Producer from three localities in Oregon; 
one lot of Rural New Yorker from Colorado; and one lot of Sir Walter 
Raleigh from Michigan; and six lots of healthy potatoes—one each of 
Burbank, Uncle Sam, and Gold Coin from Oregon, and one each of 
Burbank, Rural New Yorker, and Irish Cobbler from Wisconsin. These 
tubers were tested for the presence or absence of organisms in the stem- 
end vascular region in the following manner: The potatoes were weighed, 
numbered, washed, treated with mercuric chlorid 1 to 1,000 for two 
hours, rinsed through two lots of boiled and cooled water, spread out for 
one day in the laboratory to dry, placed in clean paper bags, and later 
cultured as follows: With a flamed and cooled scalpel a small cone of 
tissue about ^2 inch in diameter and inch deep was removed from 
around the point of stolon attachment. With another flamed and cooled 
scalpel a piece of the inner exposed vascular tissue, together with some 
surrounding parenchyma tissue, was taken from the discolored area 
(PI. 139, A, B) when present, or from apparently normal tissue when 
discoloration was not present. This was placed in a test tube containing 
a moist sterilized sweet clover stem and incubated in the laboratory 
exposed, to strong north light. As a rule a pure culture of whatever 
organism was present was secured (PI. 141, B), though occasionally 
more than one organism was isolated. These organisms could often be 
identified directly from the original isolation culture, though always in 
the case of Fusarium spp. transfers were made to tubes of sweet clover 
stems, steamed potato cylinders, and steamed rice for final identification. 
By means of growth characters, colors, and characters of the spores which 
developed on these media, many of the species, including F. oxysporum , 
F. radicicola, F. solani (Mart.) Sacc., F. discolor App. and Wollenw., 
F. discolor var. sulphureum (Schlecht.) App. and Wollenw., F. coeruleum 
(Lib.) Sacc., and F. culmorum (W. G. Sm.) Sacc. could be determined 
by the methods of Wollenweber (13) 1 and Carpenter (2). Occasionally 
other species of Fusarium were encountered with which the author was 
not familiar and which were not determined. 
After taking cultures the tubers were then prepared for planting. All 
tubers weighing 3 ounces or less were planted whole; those weighing 
from 4 to 7 ounces, inclusive, were divided into two lots, one lot being 
cut transversely into stem and eye halves and the other longitudinally 
into right and left halves; and those weighing 8 ounces and over were 
cut longitudinally and transversely into quarters (PI. 139, C). All 
1 Reference is made by number (italic) to “Literature cited, 
p. 847-848. 
