428 



EMBRYO OF DICOTYLEDONES 



monocotyledons and this feature will be seen to characterize the 

 higher members of many of the orders. 



The most characteristic feature of the dicotyledons is the 

 embryo which usually consists of a root, stem, and two laterally 

 attached cotyledons. The region of the stem above the cotyle- 

 dons is known as the epicotyl and frequently appears as a minute 

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

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



B 



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 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 

 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. 



