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. sativa and M. lupulina. 
In various fruits and in naany 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 Californica 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 
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