INTRODUCTION 297 



give many aberrant forms. A very common one under greenhouse 

 conditions is a form with very short internodes and very small leaves. 

 This is presumed to be the form which Southworth mistakenly reported 

 as a hybrid between M. saliva and M . lupulina. 



In various fruits and in many flowers the crossing of species has 

 yielded many valuable varieties. Some cases among flowers will be 

 discussed in the following chapter. Among tree fruits the next hybridi- 

 zers of species after Bull were the men who undertook to combine the 

 hardy character of the Russian apples, which had been introduced during 

 the 80's. Dr. William Saunders, then Director of the Dominion Experi- 

 mental Farms, began this work in 1894. Similar work, with apples, 

 cherries, plums, etc., has been carried on very extensively, and already 

 with important results, by N. E. Hansen of the South Dakota Experi- 

 ment Station. The production of a list of peach varieties adapted to 

 the Gulf Coast States was the work of H. H. Hume, then of the Florida 

 Experiment Station, and of P. J. Berckmans in Georgia. This was 

 accomplished largely through the hybridization of the Chinese Saucer 

 or Peen-to peach, Amygdalus platycarpa, with commercial varieties of 

 the common peach, Amygdalus persica. The work of Webber and 

 Swingle with crosses between various species of Citrus has received inter- 

 national recognition, not only because of the results secured but on 

 account of the possibilities in the improvement of citrous fruits which it 

 revealed. The production of aphis-resistant plums among hybrids of 

 distinct species, as reported by Beach and Maney, exemplifies an impor- 

 tant line of attack in breeding disease-resistant plants. 



No small part of Luther Burbank's fame is due to his success in 

 crossing species. Among the many interspecific hybrids which he pro- 

 duced should be mentioned plumcots (hybrids between plums and apri- 

 cots), the Royal walnut (Juglans Calif ornica X J. nigra), the Primus 

 and Phenomenal berries (hybrids between species of Rubus), many valu- 

 able plums and a host of flowering plants. In his work with plums, 

 as well as in the production of certain flower novelties, Burbank practised 

 composite hybridization. An illustration taken from de Vries' account 

 of Burbank's work, is the pedigree of the Alhambra plum, shown in Fig. 

 119. 



An equally if not more important phase of Burbank's work is his 

 discovery of novelties and his perfection of the same by means of selection. 

 His method is hardly to be classified as mass selection, nor is it line selec- 

 tion in the strict sense. An important feature has been the use of very 

 large numbers of seedlings either of introduced species, commercial 

 varieties, or his own hybrids. It is by the use of his unusual power of 

 observation, which Wickson thinks amounts to a gift of intuition, in 

 choosing say a dozen seedlings from as many thousand, that this one man 



