No. 604] SHORTER ARTICLES AND DISCUSSIONS 



241 



The correlation of these data, somewhat smoothed by Jones,^ 

 with a series of determinations of the percentage growth of the 

 fungus on tubers j?i the laboratory has already been determined.' 

 For laboratory growth and loss on clay loam, r= .584 zb .059. 

 For laboratory growth and loss on sandy loam, r=. 594 ±.055. 



Taken as a whole these correlations indicate (a) that suscep- 

 tibility to both early and late blight and to scab differs greatly 

 from variety to variety, and (6) that, so far as the evidence goes, 

 the varieties differ more in resistance to tuber injury than to 

 foliage infection by early blight. 



It is not at all necessary that the correlations be drawn be- 

 tween the amount of iii.jui-y to tlic same organs of the plant or 

 by tbe same disease. In many in^taiii-fs tbe so-called cross cor- 

 relations yield valuable results. 



For examplfci Stuarf discusses the question of the relationship 

 between vine infection and tuber rot. The point may be sub- 

 jected to a statistical test by correlating between the maximum 

 percentage of foliage affected by late blight as given in his 

 Table V for potatoes grown on sandy loam soil in 1905 and per- 

 centage of rot as recorded in his Tables VI and VII. Unfortu- 

 nately, the percentages are available for the vines for sandy loam 

 soil only (Table V) while the figures for tuber rot are given for 

 both sandy loam and clay loam soil. Both correlations may be 

 worked out. I find : 



For percentage foliage infection on sandy loam soil and per 

 cent, tuber rot on sandy loam soil 



i^...l31. r .316 ± .053. 



For percentage foliage infection on sandy loam soil and per 

 cent, tuber rot on clay loam soil 



In both cases tli.^ coftvl.'it imis ;iiv po^itiv*'. and licm-c .such evi- 

 dence as they I'ui'nish indicat^'s that the vai'ictifs which show 

 the greatest infection of the leaves actually an> tlu" worst to rot. 

 That the correlation between injury to tlio tops and tuber rot is 

 higher on the sandy loam soil is not ;it all sui-!)iMsing, since the 



