278 Journal of Agricultural Research voi.xx.no.4 



The notes from which these data have been compiled were obtained 

 jointly by Venus W. Pool, M. B. McKay, H. G. MacMillan, R. D. Rands, 

 and the writer during the spring and summer of 191 5. The writer wishes 

 to make full acknowledgment to these associates and to assume the 

 entire responsibility for the construction placed on the notes and the 

 deductions made from them, as well as for the accuracy of the tabula- 

 tions and compilations presented. 



OUTLINE OF METHODS AND WORK 



The general plan followed in the work may be outlined briefly as 

 follows: Material for experimental plantings, involving about 4 acres 

 of plots, was secured from various sources, as reported below. It was 

 treated 30 minutes in 1 to 1,000 mercuric chlorid solution and allowed 

 to dry, after which each tuber was examined for vascular discoloration 

 by removing with a flamed and cooled scalpel a shallow cone of tissue 

 with the stolon attachment at the center of its base. A record was 

 made of the presence or absence of discoloration and of the general 

 character of the discoloration when present, as slight, medium, brown, 

 dark, etc. When discoloration was found, the depth to which it pene- 

 trated in the tuber was determined by removing a wedge of tissue. 

 When browning was confined to a shallow area around the removed cone 

 it was designated by recording the symptom A. If the discoloration 

 extended to a greater depth, involving up to one-fourth the length of the 

 tuber, symptom B was recorded. A deeper discoloration was designated 

 by C. Discolored tubers were submitted to culture. In general one 

 planting of tissue was made from each region involved in discoloration. 

 As a rule, therefore, one planting was made from tubers showing symp- 

 tom A, tw r o from those showing symptom B, three from tubers showing 

 symptom C, and none from those showing no discoloration. In the 

 actual prosecution of the work, however, certain deviations from the 

 general rule were introduced, either to check the dependability of re- 

 sults or to secure additional information. The tubers of each lot were 

 weighed and numbered consecutively in the order of their respective 

 weights, which were recorded. With the exception of lot No. 3, the 

 tubers of each lot weighing less than 3 ounces were divided into two 

 groups, one comprising all the even numbers and the other all the odd 

 numbers. Those weighing 3 ounces or more were halved from stem to 

 apex, one half being placed with the small tubers of even number and 

 the other half with the small tubers of odd number. When the half 

 tubers weighed 3 ounces or more they were cut into stem and apex 

 portions. In a few cases the half tubers were so large as to yield stem, 

 middle, and apex pieces, or even stem, two middle, and apex pieces — 

 four in all from each half. The minimum seed piece for cut tubers was 

 \\i ounces. 



