DEVELOPMENT OF PLANTS 



413 



bud, the so-called plumule. The region of the stem below the 

 cotyledons, the hypocotyl, terminates in the root (Fig. 296). 

 The elongation of the basal portion of the hypocotyl frees the 

 root from the seed and the growth of the upper region of the 

 hypocotyl pushes up into the air the cotyledons and growing point 

 or epicotyl. The formation of the stem is sometimes due to 



Fig. 296. Structure of dicotyledonous seeds: A, nearly mature seed of 

 Lepidium. The embryo consists of the hypocotyl, hy, ending below in the 

 root, r, and the root cap and above the epicotyl, pi. Two cotyledons, c, 

 arise laterally from the stem; /, funiculus; mi, micropyle; in, integuments; 

 en, remains of endosperm. B, section of seed of water lily — e, embryo with 

 two cotyledons attached laterally to the minute stem of the embryo and sur- 

 rounded by a layer of endosperm cells; mg, sporangial cells or perisperm; i, 

 integument. 



the elongation of the epicotyl alone, the cotyledons frequently 

 containing the storage foods for the nourishment of the young 

 plant and remaining buried in the seed. 



In endospermous seeds it should be noted that the cotyledons 

 are not developed as digestive and absorbing organs as observed 

 in the monocotyledons (page 386). The primary root often per- 

 sists, forming the main or tap root of the plant, which manner of 

 growth is not so common in the monocotyledons. The Dicoty- 



