16 BULLETIN 195, U. S. DEPAETMENT OF AGKICULTUEE. 



from which 10 plants were obtained. It is evident from these fig- 

 ures that the pollen of Keeper was much more potent than that of 

 Venezuela. 



VARIETAL AFFINITY. 



It is apparent to those familiar with plant breeding that certain 

 types or strains of a given class of plants possess greater sexual affinity 

 for each other than do other types, or strains which are apparently 

 as closely related. This phenomenon has been observed by potato 

 breeders and has been taken advantage of in making crosses. One 

 of the most interestmg observations upon this point that has come 

 to the •writer's attention is that made by Taylor/ who says: 



Careful experiments this season with, that fine potato named Factor have proved 

 that it is not only sterile to its own pollen, but also sterile to all the Up-to-Date type, 

 of which class Factor is probably the best example. ... It will cross with some 

 of the colored-skinned varieties, which have also flowers of a similar tint, but the 

 seed vessels mature very slowly and never attain a large size. Where pollen of 

 white-flowered sorts can be obtained, such as the Admiral, Provost, Abundance, and 

 Cumberland Ideal, a good set can be obtained on Factor and the pods soon attain 

 full size; indeed, the growth of the so-called "plum" is remarkable in comparison 

 with that of the others aheady noted . . . the pollen of Factor has been found to be 

 absolutely sterile to some 30 other varieties of potatoes having flowers and tubers of 

 different colors and none of them of the Up-to-Date class. 



In this connection, Findlay^ says of the Up-to-Date potato: 

 Its organs of reproduction are 90 per cent of them malformed. The stamens or 

 pollen cases are small and never, so far as I have seen, contain one grain of pollen. 

 The pistil is also of the same character. . . . the Up-to-Date potato beat me off 

 so far as being able to effect my purpose, compelling me to fall back, as a last resource, 

 on its male parent, or rather a natural seedling from the same. I then effected my 

 object, and got two or three plums. But, as showing how much the Up-to-Date was 

 off this job of seed production, the plums were small, containing few seeds, and of 

 these few only about 53 per cent germinated. 



The following data obtained from crosses made in 1909 seem to 

 fully corroborate the observations made by Findlay with respect to 

 the poor seed-bearing qualities of the Up-to-Date (Table I). From 

 155 hand-pollinated flowers of this variety, only 23 seed balls were 

 secured, and one of this number was found to be seedless. The 

 seeds secured from the 22 successful crosses produced only 671 

 tuber-bearing seedlings, or an average of a little over 30.5 tuber- 

 bearing plants per berry. Seven pollen parents were used in mak- 

 ing the crosses, and three of these, the Norcross, Empire State, and 

 Fuerst Bismarck, did not produce a single seed ball. These are 

 varieties that produce pollen very sparingly or not at all. Successful 

 crosses were secured with Keeper, Early Silverskin, Irish Seedling, 

 and Round Pinkeye, all of which produce pollen abundantly. The 

 Irish Seedling gave the highest percentage of successful crosses 

 (41.2 per cent), but for some reason produced a woefully small 



1 Taylor, G. M. The cross fertilization of the potato. In Gard. Chron., v. 48, 3d ser., 1910, p. 279. 



3 Findlay, A. The potato: Its history and culture. In North British Agriculturist, Jan. 25, 1905, p. 17. 



