448 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 underground. When 

 kept warm and moist the seed absorbs water and swells, 

 the radicle makes its way out of the micropyle, the testa 

 bursts, and the plumule makes its way upwards, the epi- 

 cotyl, or part between the cotyledons and the first foliage 

 leaf or leaves, circumnutating and emerging 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 discussed 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 under- 

 ground this process is called hypogean germination. In 

 the other method that of the so-called epigean germina- 

 tion 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 the nutritive matter is 



