212 PLANT-BREEDING 



be rejected. The casual inspector cannot discern them, and 

 moreover he is simply bewildered by the profusion of lus- 

 cious fruits which are tempting his eyes and palate on all 

 sides. 



Among the American species of the large plum genus, the 

 beach plum or Prunus maritima plays a prominent part in 

 Burbank's crossings on account of the small demands it makes 

 on soil and water. It is one of the most common shrubs 

 along the eastern shores, growing everywhere on the coast 

 or along the larger rivers, in dense bushes. It is very pro- 

 ductive and is satisfied with almost any life conditions. It 

 thrives as abundantly on dry and sandy plains as where the 

 soil is covered by salt or fresh water during part of the year. 

 Tt abounds in varieties having red or blue or yellow prunes, . 

 sometimes large and sometimes small, ripening early in some 

 locaHties and late in others, affording thereby a rich material 

 for selection and hybridization. The prunes are often as 

 small as huckleberries and are gathered onl\' for preserving 

 purposes, but it blooms a month after most of the other 

 species and is thereby almost free from the danger of having 

 its blossoms destroyed by frost while it proceeds with the 

 ripening of its fruit until late in the fall. 



All these notable quahties Burbank has tried to transmit 

 to his hybrids, combining them with the usual requirements 

 of palatable plums. By successive crosses and correspond- 

 ing selections, the bush form of the beach plum has been 

 eliminated from the hybrid strains, upright trees having 

 been preferred for the further crosses. Stones as small as 

 those of the cherry, in plums of full size are another result 

 of these combinations. The first generation of the original 

 crosses were, of course, only of relative value, but by re- 

 crossing them with as manv varieties and hvbrids as were 

 available, an extremely rich material for selection has been 

 secured. 



