290 Journal of Agricultural Research voi.xx.No. 4 



It appears further from the data given on the second and third groups 

 in Table V that a tuber from healthy parentage or from fungous-invaded 

 parentage is more likely to yield a diseased plant from a stem-end seed 

 piece than from the apex. Two hundred and fifty-eight tubers yielded 

 diseased plants from stem ends and 1 50 yielded diseased plants from apex 

 ends. One hundred and twenty-five of these tubers yielded diseased 

 plants from both stem and apex. The ratios, therefore, of stem, apex, 

 and pairs were approximately 10:6:5. The fact that the proportion of 

 diseased stem plants to diseased apex plants is slightly higher in the 

 healthy group than in the parasitic disease group is not inconsistent with 

 other data presented in this paper. 



The facts seem to indicate that the greater liability of stem-end plants 

 to disease results not because the vascular tissue of the seed piece is more 

 often infected by fungi but because it is more often endowed with less 

 physiological resistance. 



DISEASE AND RECOVERY 



Data dealing with disease and recovery are presented in Table VI. 

 The total number of plants reported at the first note taking as diseased 

 is recorded in the first column. Following this is recorded the number 

 of these plants which subsequently appeared to recover and to remain 

 healthy. The next column gives the number of additional plants re- 

 ported diseased at the second note taking, followed similarly by the 

 number of those which subsequently recovered. The next column 

 records the number of hitherto healthy plants which appeared to be 

 diseased at the third note taking. 



In the lower portion of the table the Rural New Yorker and the Pearl 

 varieties have been summarized in juxtaposition for purposes of con- 

 venient comparison. The outstanding feature of this table is the re- 

 markable degree of recovery shown, particularly in Colorado. This is 

 especially noticeable with the Pearl stock in Colorado. It is, possibly, 

 the ability of the Pearl to recuperate in that section which accounts for 

 the popularity of this variety in the G: seley region. 



A summary of the data on disease and on recovery for the entire 

 experiment in total and by States is given in Table VII. Table VIII 

 shows percentage data figured from information shown in Tables IV 

 and VII. Attention is directed to the figures in Tables IV and VII in 

 connection with the percentage averages in Table VIII, because per- 

 centage figures may be misleading when the numbers from which they 

 are computed are small. A striking example of this is shown in Table 

 VIII, where one plant in Wisconsin was diseased and did not recover, 

 while two were diseased in Colorado and both recovered. This appears 

 in the respective columns on recovery as o and 100 per cent. In the 

 larger groups and in the aggregates, however, reduction to percentage 

 gives a clearer presentation of the facts. 



