PLANT BREEDING 177 
in this respect, so that it is sometimes necessary to select 
only about one best beet out of every thousand to grow seed 
for the next crop. 
In the case of plants grown for the production of seed of 
standard varieties for the market, as beans, peas, or any of 
the many flowers (such as sweet peas), in regard to which 
there is much competition, great attention is paid to weeding 
out and destroying plants that do not conform to the standard. 
This process is called roguing. The maintenance of the breed 
depends largely upon the intelligence and thoroughness with 
which it is carried out. 
168. Ancient and modern plant breeding. No one knows 
when plant breeding began, because the earliest attempts of 
man to cultivate useful plants date back to unknown antiquity, 
and it is highly probable that the first growers of plants for 
human food more or less unconsciously selected the best seeds 
to be sown for a new crop, and were thus really practicing 
plant breeding. Among the Chinese, agriculture began at 
least 4600 years ago, and for a considerable part of that time 
they have paid much attention to the perpetuation of desirable 
varieties of the plants of the farm and garden. 
Modern plant breeding did not begin at anv definite date. 
Some valuable work was done in selecting and propagating 
improved varieties of wheat in Great Britain as early as the 
first quarter of the nineteenth century, but it was not until 
toward the middle of the century that many investigators 
began to try to put plant breeding on a scientific foundation, 
working with plants ranging all the way from the cereals to 
sugar beets. One of the main problems in plant breeding is 
that of predicting the way in which the characters of a plant 
will be inherited by its descendants. In a large number of 
cases, a number which is rapidly increasing, it is possible to 
make such predictions with scientific accuracy. These are 
based on the immense mass of data which has been gained 
from tens of thousands of experiments made by scientific 
investigators and by practical plant breeders everywhere. 
