CORN KERNEL 



63 



cot 



re 



The location of the embryo at one side of the endosperm, instead 

 of being centrally located and surrounded by the endosperm, is a 

 peculiar feature of the Grass type of seeds. 



The embryo consists of two main parts : the large scutellum or 

 cotyledon (cot) which lies in con- 

 tact with the endosperm, and the 

 embryonic axis which upon germi- 

 nation produces the stem at its 

 upper and roots at its lower end. 

 The axis is attached along its 

 central region to the cotyledon, 

 which supplies it food during 

 growth. At the upper end of the 

 axis is the plumule, a small bud- 

 like structure consisting of a grow- 

 ing point (gr) and some small 

 leaves (I). The plumule is en- 

 closed in a sheath (ct) called col- 



eoptile. Between the plumule 



, , , . , FIG. 66. Section through a ker- 



and the attachment of the coty- nel of Corn . cot) coty iedon; ep, epi- 



ledon is a short stem (st), which thelial layer of cotyledon; ct, coleop- 



with the plumule is often called tile; gr, growing point of plumule; 



epicotyl (the portion above the ^ young leaves ; st, epicotyl; r, radi- 



cotyledon). The portion of the cle ' rc > root ca P' cr > coleorhiza ; "> 

 . , , , , . i j , soft endosperm; h. hard endosperm; 



axis below the cotyledon consists ^ covering called pericarp Much 



chiefly of the radicle (r), the struc- enlarged. 



ture which develops the first root. 



The radicle bears at its tip the root cap (re) and is enclosed by 



the coleorhiza (cr). 



The hypocotyl, which is all or only a part of the axis between the 

 plumule and radicle (a point in dispute among botanists), is the 

 portion of the axis developing least when the embryo resumes 

 growth. In the Grasses there is very little elongation of the hypo- 

 cotyl and, consequently, the establishment of the young plant in 

 the soil and light depends mainly upon the growth of the radicle 

 and plumule. The fact that the hypocotyl remains small while 

 the radicle, since it forms the first root, becomes a prominent 

 structure, accounts for the general application of the term rad- 

 icle to all of the lower portion of the axis, and the rare use of the 

 term hypocotyl in connection with grass embryos. 



