OF THE EMBRYO AND SEEDLING. 



25 



carries up the light seed far above the surface of the ground, the 

 tip only remaining in the albumen of the seed until that is ex- 

 hausted, when the tip perishes and the emptied husk falls away. 

 About this time the plumule shoots forth from one side of the 

 subterranean base of this cotyledonar leaf, in the form of a second 

 and similar filiform leaf, to be followed by a third, and so on. 

 The sheathing bases of these succeeding leaves become the coats 

 of the Onion-bulb. The internodes remain undeveloped until the 

 plant is ready to blossom. Very similar is the germination of 

 a date-seed, except that the 

 protruding cotyledon does 

 not lengthen so much, nor 

 does it elevate the heavy 

 seed. Instead of the seed 

 being carried up, the lower 

 end of the embryo, contain- 

 ing the plumule, is pushed down more or less into the loose 

 soil, from which in time the developing plumule emerges. 



41. The embryo of Grasses, especially of those which yield 

 the cereal grains, is more complex, owing mainly to the great de- 

 velopment of the plumule 

 and the manner in which e - 

 its rudimentary leaves 

 successively enclose each 

 other. That of Maize or 

 Indian Corn, one of the 

 largest, is most convenient 

 for study. (Fig. 56-59.) The floury part of the seed, which 

 makes most of its bulk, is the albumen, largely composed of 

 starch. The embryo is exterior to this, applied to one of its 

 flat sides, and reaching from the thinner edge to or above the 

 middle in the common variety of corn here represented. The 

 form of the embryo is best shown, detached entire, in Fig. 58 : 

 its structure appears in the sections. The outer part is the 

 cotyledon, which incompletely enwraps the plumule : it adheres 

 closely to the albumen by the whole back, and remains un- 

 changed in germination : its function is to absorb nutritive 



FIG. 56. Section, flatwise, of a grain of Indian Corn, dividing the albumen and the 

 embryo. 57. Similar section at right angles to the first. 58. A detached embryo : 

 corresponding parts of Fig. 57 and 58 indicated by dotted lines. 



FIG. 59. Vertical section of Indian Corn across the thickness of the grain, dividing 

 the embryo through the centre and displaying its parts : c, cotyledon ; p. plumule ; 

 r, the radicle or caulicle. 



FIG. 60. Similar section of grain of rice. 61. Same of an oat-grain ; the parts 

 as in Fig. 59. 



