No. 604] SHORTER ARTICLES AND DISCUSSIOXS 239 



the past several years at the Vermont Agricultural Experiment 

 Station. 



In a recent bulletin Stuart^ summarizes the data obtained dur- 

 ing five years' observations on percentage infection by early 

 blight (Alteniaria solani). In his Table I he gives the estimated 

 percentage infection in a series of varieties during the period. 

 Since during a portion of the experiment all the varieties were 

 not considered, I have calculated the correlations in two groups. 

 In one case i\^=149, in the other 7V^ = 50. The smaller group 

 comprises only varieties also included in the larger. The corre- 

 lations, calculated by the usual product moment method^ with- 

 out grouping, appear in the accompanying table.^ 



Correlation tor Vine Resistance to Early Blight in Two Years 



1905-1906 + .055 ± .055 — .056 ± .095 



1905-1907 + .438 ± .045 + .420 ± .079 



1905- 1908 — .021 ± .095 



1906- 1908 — ■ +.323 ±.085 



Only 2 of the 9 constants are negative ; these are insignificant in 

 comparison with their probable errors. All the constants which 

 have substantial values and are materially larger than their prob- 

 able errors are positive in sign. The average of the two negative 

 constants is —.038, of the seven positive coefficients +.227, and 

 of all the (unweighted) values + .168. Thus there is clearly a 

 measurable differentiation of the varieties in respect to suscep- 

 tibility to Alternaria. 



The values are, however, exceedingly variable, ranging as they 

 do from — .056 to -f -438. The great variation in the actual 

 constants I am inclined to attribute to (a) the difficulty of esti- 

 mating the percentage of infection, (&) the unavoidable experi- 

 mental errors associated with relatively small cultures, and (c) 

 the wide variation in average percentage infection from year to 

 year. Both (a) and (&) are factors which tend to render the 

 actually recorded percentages somewhat erroneous as measures of 

 the real susceptibility of the variety, and tend in consequence to 

 dilute the strength of the correlation. With respect to the third 



3 The chief (liscror;incy l. tur, n \\w n-ults lor thi> lar^'er ( -V :^ 149) and 

 for 1906 and 1907 whero tlu" two .■orrH.it ions nro .012 ± .05r> and .226 ± 



