32 NATURE STUDY AND AGRICULTURE 
13. Spring wheat is put in much earlier than corn because it stands 
cold weather better, and for the same reason peas may be planted earlier 
than beans. Frost also injures corn and beans more readily than wheat 
and peas. 
14. Seeds should be kept in a cool, dry room over the winter. To 
keep them damp is injurious, and if they are frozen while wet, the injury 
is often quite serious. If they are dry it does not harm them to freeze. 
To keep them over the winter in a well warmed room where the at- 
mosphere is at the same time very dry also lessens their vitality. Try 
to demonstrate some of these points by experiment. 
15. Seeds will sprout in the dark, else they could not come up when 
planted in the ground. But the growing plant needs sunlight. Plants 
grown in the dark never look green and can grow only by consuming 
the nourishment which is stored up within them or within the seed. The 
green coloring matter and sunlight are necessary for the production of 
new plant substance out of the raw materials taken from the atmosphere 
and the soil. 
16. As a rule, seeds should not be covered deeper than is needful 
to insure sufficient soil moisture, but for the sake of this moisture it is 
often desirable to plant them as deep as their nature permits. Seeds 
that come up with thick seed leaves, as beans and radishes, should not 
be covered more than about five times their thickness; while those that 
do not push their seed leaves to the surface, as peas and corn, wheat and 
other grains, may be covered ten times their thickness. Of course, in a 
loose soil they may be planted deeper than in soil that is apt to become 
hard. 
17. The vitality of seeds diminishes as they become older, and after 
a certain age they lose altogether their power to germinate. Thus, 
go per cent of cucumber seeds may germinate when they are a year 
old, 75 per cent when two years old, 70 per cent when three years old, 
and so on, —a small percentage germinating when they are as old as 
ten years. The age limit of the seeds of most cultivated plants is shorter 
than this. Thus, Indian corn and onion generally live but two years; 
turnip, radish, and cabbage, five years; bean, pumpkin, squash, and 
watermelon, six years. 
18. Farmers are generally careful to clean their seed grain so as to 
reject all kernels that are under size or under weight. The plump, 
