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 



