78 The Potato 



set seed. Salaman ^ estimates that only 5 per cent of 

 his crosses set seed. East - found it difficult to get a 

 good setting of seed in very dry seasons. 



In some cases, persistent attempts have finally resulted 

 in a successful cross where at first it seemed impossible. 

 A second drawback is the scarcity of pollen. Many 

 varieties produce little or no pollen and have to be crossed 

 if we are to get sexually produced seed from them. Also, 

 some plants produce yellow pollen which is sterile and 

 does not function. Other varieties rarely, if ever, flower. 



Most varieties of potatoes are already hybrid and 

 when seed from them is sown, the type breaks up into 

 many elementary forms, most of which are of no value 

 to the grower. This adds another difficulty to those 

 mentioned above. Each variety which is crossed trans- 

 mits a number of undesirable, latent characters which 

 come out in the hybrids. Often the seedlings from a 

 cross will show so many of the traits of the wild potato 

 that none of them is worthy of further attention. Se- 

 curing a valuable new variety from a cross seems in this 

 case to be largely a matter of chance. There is an ele- 

 ment of uncertainty in the work, which is not encoun- 

 tered with most crops. 



The potato flower consists of a rotate corolla of white, 

 lilac or purple petals, five green sepals, five anthers and 

 a single pistil. The style projects up through the "cone" 

 formed by the closely adhering anthers. The anthers 

 open at the tips and give out a small amount of pollen. 

 In the day time, the flower is in an erect position, and it is 

 impossible for pollination to take place. At night, how- 

 ever, the flower bends over and some of the pollen can fall 



1 Journ. Gcii., Vol. 1, pp. 7-46. 



2 Illinois Bui. 127. 



