412 EXPERIMENTS WITH PLANTS 



before the earliest of the old varieties, and, on the 

 other hand, varieties whioh last until December, the 

 Plum season has been greatly prolonged. The impor- 

 tance of early and late varieties is very great, since 

 they enter the market without competition in their 

 particular line. 



6. Some varieties have been produced which seem 

 to be unaffected by frost. Even though the petals and 

 young leaves are frozen and killed, the stamens and 

 pistils go on performing their functions and the trees 

 bear a full crop of fruit. Other varieties have been 

 obtained which are enormously productive even where 

 the old varieties fail. Many of these begin to bear 

 abundantly the third year from the seed when grafted 

 upon trees of ordinary size; others have been bred 

 to stand shipping for long distance. Some kinds 

 have been secured which remain on the tree from six 

 to nine weeks in hot weather without deterioration, 

 thus possessing a great advantage over many of the 

 older varieties which must be picked as soon as ripe. 



Some of these new Plums are accommodated to 

 climates and conditions where the Plum has hitherto 

 proved a failure. A notable instance of this is the 

 Improved Beach Plum (Fig. 233), obtained by crossing 

 the Beach Plum (Prunus maritima) with an American 

 Plum {Primus Americana). The Beach Plum is a wild 

 species growing along the coast as a low, spreading 

 shrub, not more than three or four feet high, with a 



