LESSON 21.] 



THK EMUUYO. 



137 



n?."). The embryo, being a nidimentary plantlet, ready formed in 

 tin; seed, lias oidy to grow and develop its parts to become a young 

 l)lant (ir>). Even in the seed these parts are generally distinguish- 

 able, and are sometimes very conspicuous ; as in a rumi)kin-seed. lor 

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



37 G. The Ratlicic, or rudimentary stemlet, which is -sometiirif^a jon^ 

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

 ous figures already referred to. In the seed it always 

 I)oints to the micropyle (371), or what answei-s to the 

 foramen of the ovule (Fig. 32.), 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 lolylcih)llS or Srcil-Lcaves. With these in various forms we 

 have already become familiar. The number of 

 cotyledons has also been explained to be imj)or- 

 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 



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

 lea\es, always opposite each other. In the Pine family we find a 



Puhjcotijledonous embryo (Fig. 45, 46) ; tliat 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 

 pair 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 oilier end of the radicle grows downward, 

 and becomes the root. 



FIG. 323. Embryo of the riimpkin, seen flatwise. 3D4. Same cut tlirouph and viewed 

 edgewise, enlarged : the small plumule seen between the cotyledons at their hase. 



FIG. 325. Seed of a Violet (Fij,'. 319) cut thronjih, showing the embryo in the section, 

 edgewise ; being an analropuun seed, the radicle of the straight enibryt points down to the 

 ba.se near the hilum. 



FIG. 32G. Similar section of the orlhotmpous seed of Buckwheat. Hero tiie radicle points 

 directly away from the hilnm, and to the apex of the seed ; also the thin cotyledons ha|>peu 

 ill this plant to l>e bent lound into the same direction. 



12* 



