458 VEGETABLE PHYSIOLOGY 
case of the zygote. In the Thallophytes this resting period 
is sometimes a long one; in the higher Cryptogams it is 
not so noticeable, and in the Phanerogams or Spermo- 
phytes, where the zygote is always developed inside the 
sporangium, it usually proceeds to active growth almost at 
once. In the latter plants, however, a resting period takes 
place later, after the seed is fully formed. The develop- 
ment of the young sporophyte, in fact, takes place in two 
stages, the one ending with what may be called the matura- 
tion of the seed, and the other beginning with the process 
of germination. Seeds when detached from the parent 
plant preserve their vitality for a variable length of time, 
sometimes even for years, and are capable of germinating 
freely when exposed to favourable conditions. 
The germination of the dicotyledonous seed occurs in 
one of two methods. In the first of these, the cotyledons, 
which are thick and fleshy, remain undergound. When 
kept warm and moist the seed absorbs water and swells, 
the testa bursts, and the radicle, and subsequently the 
plumule, grow out and elongate in opposite directions. In 
the growth of the young shoot the epicotyl, or part between 
the cotyledons and the first foliage leaf or leaves, circumnu- 
tates and emerges in the form of an arch, owing to the greater 
growth of one side. After reaching the air the growth 
changes, the greatest increase passing to the opposite side, so 
that the epicotyl straightens itself. During this time it 
subsists upon the nourishment stored in the cotyledons 
in the shape of reserve materials. We have already dis- 
cussed the means whereby these digestive and nutritive 
changes are brought about, the agencies which effect them, 
and the various transformations which are met with. As 
the cotyledons remain underground this process is called 
hypogean germination. In the other method—that of the 
so-called epigean germination—the cotyledons sooner or 
later rise above the ground and become green, the hypocotyl 
behaving as does the epicotyl in the first case. These are 
frequently, though not always, albuminous seeds, in which 
