Practice of Plant Breeding 
tion or hybridising, although it is perhaps infinitely 
more difficult. Some results are very unexpected. 
Muller (Thurgau) selected ten potatoes of, as nearly 
as possible, exactly equal size. Five were kept in an 
ice-house and the others in a house cellar at ordinary 
temperature. Both were planted at the same time, but 
those from the ice-house gave a large crop three months 
after planting, when those which had been kept warm 
had only begun to sprout! 
One unfortunate point about all man’s selected and 
improved varieties is that they are apparently doomed 
sooner or later either to degenerate and fall back into 
their original state, or to become so feeble in constitu- 
tion that they readily fall a prey to fungus-diseases or 
insect-attacks. 
Some practical plant-breeders doubt whether this 
must necessarily happen. There is a long discussion of 
the subject in the Journal of the Royal Horticultural Society 
for December 1906, especially with regard to potato- 
degeneration. Some excellent sorts, such as Victoria, 
degenerate quickly, and others (Dunbar Regent) have 
vanished, although they were heavy croppers and of 
an excellent quality. The best types of 1845, such as 
Buffs and Dons, are no longer to be found. 
There are, it is true, apparent exceptions, such as 
Ashleaf and Early Rose, which seem to have perennial 
youth; but these are early varieties, which would pro- 
bably escape the worst attacks of the fungus in any 
case. 
Of course when a plant is propagated continually by 
tubers, it is just the same individual plant that goes on 
living from year to year, and one would expect it to 
grow old and feeble. But 500 years is not a very 
great age for some trees, which may live to 3000 years 
or more under exceptional conditions. No variety of 
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