396 BULLETIN No. 127. [August, 



fects are obscure, and there appears to be no certain way of dis- 

 tinguishing between what might be called real correlations, which 

 are probably to a greater or less degree effects from the same in- 

 ternal cause, or where two characters are inherited as a single unit : 

 and false correlations in which one is the cause and the other the 

 effect, or in which both characters vary as the result of some ex- 

 ternal stimulus. In practical work either type may become a help 

 in its prosecution, but in studying problems of heredity, inability to 

 distinguish the type often leads to great confusion. Space cannot 

 be taken to comment upon these observations except to make the 

 statement that it has been the writer's experience that the degree of 

 correlation of any characters which he has observed, is extremely 

 variable with different varieties, on diverse types of soil, and in dis- 

 similar seasons. 



With regard to the production of plants, Arthur (2) in an 

 elaborate investigation found that the number of stalks is very 

 slightly if at all related to the number of eyes upon the seed piece, 

 provided pieces of equal weight are used. The number of stalks, 

 however, increases directly with the weight of the seed piece; and 

 with the number of stalks varies directly the number of tubers and 

 their total weight in the produce. He also and later Wollny (112) 

 state that the eyes of large tubers produce stems of a sturdier 

 growth. 



Liebscher (66) states that thin stemmed plants produce small 

 tubers and that plants with fine stems produce many small tubers. 



There seems to be no constant relationship between colors of 

 tubers and of blossoms or between dark skinned tubers and dark 

 vines, but Liebscher (66) found that profuse blossoming points to 

 late ripening, and> heavy seed setting to small tuber formation. The 

 latter statement has been a general belief but Fraser (37) states 

 that in his experience many of the heaviest yielding varieties at 

 least bloom freely. Liebscher believed seed and tuber production 

 to be physiologically opposed. Fruwirth (43 v. 3 p. 10) states that 

 Dalkowsky is of the opinion that strong power of seed production 

 is also correlated with ability to resist disease. 



Osterspey (76) found in early varieties less foliage than in late 

 varieties; and within a variety, in both early and late varieties, 

 there was a relation between number of tubers and number of 

 stalks. 



Fischer (32) found that flat-round tubers were richer in starch 

 and produced less massive plants; while long-cylindrical tubers 

 were poorer in starch and produced large straggling foliage. Fru- 



