14 BULLETIN 195; U. S. DEPARTMElfT OF AGKICULTUKE. 



Table I. — Record of potato crosses made at Burlington, Vi., in 1909 — Continued. 



Parentage of cross. 



Num- 

 ber of 

 flowers 

 crossed. 



Num- 

 ber of 

 seed 

 balls de- 

 veloped. 



Percent- 

 age of 



success. 



Number 

 of tuber- 

 bearing 

 seedlings. 



Average 

 number 

 of seed- 

 lings per 

 seed ball. 



Solarium utile Klotzsch i (wild) X Keeper . 



Solarium utile Klotzsch X Seedling 962 



Solarium utile Klotzsch X Seedling 949 



72.7 

 50 

 100 



12.5 

 15 



Total or average. 



1,599 



28.6 



18,947 



1 Called S. utile by Pierre Berthault, Recher. bot. sur le Solanum tuberosum. In Ann. de la Sc. Agron., 

 6th Arm., p. 181, fig. 1, 1911. Mexican species. 



In the first cross of the third seed parent, Professor Maerker X 

 Apollo, both the seed and pollen parents are of German origin, 

 the latter being one of the most disease-resistant varieties in 

 the collection. Nine seed balls are recorded from 12 flowers 

 pollinated and 275 tuber-bearing plants were obtained from 

 this lot, or an average of 30.6 plants per berry. Fifteen flowers 

 pollinated with pollen from Early Silverskin produced 15 seed 

 balls, from which 555 plants were obtained, an average of 37 plants 

 per berry. When crossed with Keeper, 12 seed balls were developed 

 from 13 flowers and these gave 326 plants, or an average of 27.2 

 plants per berry. Pollen from Rand's Peachblow proved ineffective. 



It is interesting to compare the results from the two crosses, 

 Sophie X Keeper and Professor Maerker X Keeper. In the first 

 instance the percentage of success is 80 and in the latter 92.3. 

 Carrying the comparison farther, however, we fijid that the first 

 cross averaged over 140 plants per berry, while the latter averaged 

 only 27.2. These data make it at once apparent that some 

 varieties develop fewer ovules than others. 



Two of the most interesting crosses in Table I are those of Sola- 

 num utile Klotzsch with seedlings 949 and 962, from which some 90 

 tuber-bearmg plants were produced. Solanum utile is a wild Mexican 

 species producing tubers rather sparingly on long, spreading stolons. 

 The tubers rarely exceed or even reach the size of a small hen's egg 

 and when well developed are of a purple color. Immature tubers 

 do not show color, and owing to this characteristic HeckeP was led 

 to conclude that he had secm"ed a mutant when white-colored tubers 

 were observed to produce colored ones. The seedlings of these two 

 crosses, while varying considerably from the seed parent, neverthe- 

 less bore a very striking resemblance to it. A number of them made 

 a much stronger and larger vine growth and produced larger tubers, 

 some of which bore a more or less distinct resemblance to the pollen 

 parent. Seed baUs were borne rather sparingly on some of the 

 seedlings. Up to the present time these seedlings offer little, if any, 

 promise except in the possibility of their possessing greater resist- 

 ance to disease. 



1 Heckel, E. M. Sur les Origines de la Poinine de Terre Cultiv^e, 

 (Seep. 71.) 



; p., illus., 8 pi. Marseille, 1907. 



