4 PLANT PROPAGATION 
which should, however, not be at such a high tempera- 
ture as to risk injury to the growing-point. Some kinds 
will not only grow more quickly, but appear to derive 
benefit through this process. It should, however, be 
remembered that when once they have been soaked in 
water they should not be allowed to become dry either 
before or after sowing—at any rate until they have 
developed a fair amount of roots and foliage. Those, 
such as Palm seeds, that are sometimes put in trays of 
water over the hot pipes in the hot-house until they 
show signs of sprouting should never be transferred to 
pots of cold soil, but have some specially prepared and 
warmed ready to receive them, so that they sustain no 
check. 
Germination. 
We understand by this term that a seed is in the act 
of sprouting or vegetating. In order to bring it about, 
the seed must be exposed to a certain temperature above 
freezing-point, according to its nature. Seeds of tropical 
plants, of course, need more heat to excite the embryo 
to activity than those natives of colder regions. There 
must also be moisture and atmospheric air. Many 
examples have been recorded of seeds that have been 
buried to a depth where the air could not penetrate 
remaining in a dormant condition until raised to the 
surface and influenced by the combined effects of heat, 
air, and moisture. For a long time a period of dark- 
ness was considered necessary to effect germination, 
but later investigations have proved that this is 
erroneous in at least some instances. 
Some seeds with very hard shells, such as various 
Nuts, Nelumbiums, Cannas, certain Palms, and many 
