86 A TEXT-BOOK OF BOTANY 
of the hypocotyl is a bud, called the plumule, from which 
the future leafy stem is to develop. In many seeds the 
reserve food is not stored in the cotyledons, but in a spe- 
cial tissue surrounding the embryo, which in general may 
be called endosperm. In the violet seed, for example, 
within the testa is the endosperm, and embedded in the 
endosperm lies the embryo (Fig. 81a). 
44. Conditions for germination.—The length of time 
seeds may retain their vitality varies with different plants. 
In nature they are expected to germinate in the growing 
season following their maturity; but many are known to re- 
tain the power of germination for several years if kept in 
proper conditions, chief among which, apparently, is dry- 
ness. The stories of the germination of wheat and corn ob- 
tained from the wrappings of mummies have proved to be 
myths. 
The conditions required for germination are abundant 
moisture, suitable temperature, and a supply of oxygen 
(which means access of air). Seeds vary greatly in the 
amount of heat necessary for germination, as may be 
inferred from the fact that some seeds germinate in early 
spring or even on the melting snow-fields of alpine and 
arctic regions, while others need the heat of the tropics. 
45. Absorption of water.—When a seed has been placed 
in the proper conditions for germination, the first visible 
result is its swelling through the absorption of water. The 
amount and force of this swelling may be observed by plac- 
ing a quantity of seeds in a tumbler of water and putting 
various weights on the mass. It is entirely clear also that 
oxygen has been passing in, for the seed gives off carbon 
dioxide and heat. That heat is given off by a germinating 
seed is made very plain in the process of malting, in which 
a large mass of barley is put in germinating conditions in a 
confined space, and the combined heat from all the seeds 
becomes very evident. 
