THE BREEDING OF COLD-RESISTANT FRUITS. 403 
seven months for maturity, and attains a height of twenty feet, while at 
its northern limits it is five feet or less in height, and takes less than 
three months for maturity. This work was done by Indians long before 
the advent of the white man. It will be noticed that the plant has not 
lost its need for a high degree of heat during its ripening period, and has 
not increased its power of resistance against frost. In the winter-time 
the dry seed, if kept dry, will resist any degree of cold. The plant, in 
other words, has been shortened in season only, and not changed in its 
capacity to endure cold. 
It is now quite evident, from a survey of the whole field, that hardiness 
cannot be obtained by selection alone. This is the work for Nature, not 
man, to undertake. It is unprofitable for him to begin a labour that 
takes many thousands of years for completion. But hardiness can be 
obtained by crossing with a hardy species. 
As to hardiness being a Mendelian character, I know not. In our 
work of selection hitherto we have insisted on large size and good quality 
of the fruit, as well as hardiness, which has compelled the destruction of 
thousands of inferior-fruited seedlings which were hardy ; and in plants pro- 
pagated by budding and grafting it has not been necessary to fix the type. 
That hardiness can be transferred, by crossing a tender species, now 
admits of no question. For example, my hybrids of the wild prairie straw- 
berry with the French ever-bearing type survive, while the French parental 
type the winter kills. The hybrid of Western sand cherry with a Chinese 
apricot is hardy, while the Chinese species (Prunus Simoni) is winter- 
killed. . 
The question arises—‘‘ What is hardiness?”’ Some fifteen years ago 
the Iowa State Horticultural Society had an investigation conducted to 
determine the nature of hardiness in the apple. Chemical examinations 
were made of the wood of hardy and tender varieties ; the cell structure 
was examined under high powers of the microscope, and the number of 
palisade cells in the leaf was investigated. All led to negative results. 
It would be a great advantage to be able to determine by chemical or 
histological examination as to whether a new variety of apple would 
prove hardy in our test winters, but we must regard the problem as un- 
solved. Hardiness can be transmitted; it is something intangible to 
superficial examination, but inherent in the plant itself. 
The United States Department of Agriculture has extended the citrus 
fruit belt northward, by hybridising the cold-resistant Citrus trifoliata of 
Japan with choice sweet oranges. This work is of the greatest possible 
value, and incidentally illustrates this same possibility of hardiness being 
imparted by crossing with a hardy species. 
There is a limit to the northward extension of the cultivated apple 
(Pyrus Malus) even by the hardiest representatives of the Russian race. 
This is very likely determined by the cold-resistant capacity of the 
indigenous race of Pyrus Malus in Russia itself. To extend the apple 
limit north-westward it will be necessary to hybridise with the pure 
Siberian crab (Pyrus baccata) ; this is now being done in many places. 
The work of Thomas Andrew Knight one hundred years ago in England, 
would help in this work, were it possible to find the hybrids of this 
ancestry which he originated at that time. However, from the thousands 
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