LESSON 21.] 



THE EMBRYO. 



137 



pi 



ab 



r* 



375. The embryo, being a rudimentary plantlet, ready formed in 

 e seed, has only to grow and develop its parts to become a young 



lant (15). Even in the seed these parts are generally distinguish- 

 able, and are sometimes very conspicuous ; as in a Pumpkin-seed, for 

 example (Fig. 323, 324). They are, first, 



376. The Radicle, or rudimentary stemlet, which is sometimes long 

 and slender, and sometimes very short, as we may see in the numer- 

 ous figures already referred to. In the seed it always 



points to the micropyle (371), or what answers to the 

 foramen of the ovule (Fig. 325, 326). As to its po- 

 sition in the fruit, it is said to be inferior when it points 

 to the base of the pericarp, superior when it points to 

 its summit, &c. The base or free end of the radicle 

 gives rise to the root ; the other extremity bears 



377. The Cotyledons OF Secd-Leaves, With these in various forms we 

 have already become familiar. The number of 



cotyledons has also been explained to be impor- 

 tant (32, 33). In Corn (Fig. 40), and in all 

 Grasses, Lilies, and the like, we have a 



Monocotyledonous embryo, namely, one fur- 

 nished with only a single cotyledon or seed-leaf. Nearly all the 

 rest of our illustrations exhibit various forms of the 



Dicotyledonous embryo ; namely, with a pair of cotyledons or seed- 

 leaves, always opposite each other. In the Pine family we find a 



Polycotyledonous embryo (Fig. 45, 46) ; that is, one with several, 

 or more than two, seed-leaves, arranged in a circle or whorl. 



378. The Plumule is the little bud, or rudiment of the next leaf or 

 ir of leaves after the seed-leaves. It appears at the summit of 



the radicle, between the cotyledons when there is a pair of them, 

 as in Fig. 324, 14, 24, &c. ; or the cotyledon when only one is 

 wrapped round it, as in Indian Corn, Fig. 40. In germination the 

 plumule develops upward, to form the ascending trunk or stem of 

 the plant, while the other end of the radicle grows downward, 

 and becomes the root. 



:- 



cd 

 ba 



di, 



FIG. 323. Embryo of the Pumpkin, seen flatwise. 324. Same cut through and viewed 

 wise, enlarged ; the small plumule seen between the cotyledons at their base. 



FIG. 325. Seed of a Violet (Fig. 319) cut through, showing the embryo in the section, 

 edgewise ; being an anatropoua seed, the radicle of the straight embryo points down to the 

 base near the hilum. 



FIG. 326. Similar section of the orthotropous seed of Buckwheat. Here the radicle points 

 directly away from the hilum, and to the apex of the seed ; also the thin cotyledons happen 

 in this plant to be bent round into the same direction. 



12* 



