THE EMBRYO CONTINUED. 



11 



LESSON III. 



THE EMBRYO CONTINUED— GEKMINATION— TORUS. 



21. Seed, Embryo. 22, 23. Emit, Seed. 24. Cotyledons. 25. Ger- 

 mination. 26. Oollum. 27. Axis of growth, or Torus ; Houses. 



21. Seed. Embryo. — The ovule, after fertilization, is 

 technically called a Seed. The embryonic vesicle — which 

 is equivalent to the oospore in Cryptogamia — does not re- 

 main a simple cell. It rapidly multiplies its cells by divis- 

 ion ; the cells remain united (Fig. 3, C), and are gradually 

 differentiated — that is, changed into different organs and parts 



Fig. 6. — A, vert, section of grain of Oats {Avena\ 

 with large perisperm ; a, cotyledon with its pointed 

 scutellum, or sihield; g, plumule; r, radicle. B, em- 

 bryo removed and still more enlarged ; a, scutellum ; 

 c, cotyledon ; /, slit through which the plumule will 

 pass out in sprouting ; r, radicle. O, grain of Wheat 

 {Triticnm) sprouting; </, seed ; /, plumule ; r, coleo- 

 rhiza, or root-slu-ath. D, grain of Indian Corn (2ea) sprouting; plumule with 

 three leaves ; stem sending out adventitious roots above the collum. 



like those of the parent plant. Whilst this process is going 

 on in the embryo itself, the embryo-sac becomes filled 

 with nutrient substances which are provided to sustain the 

 embryo at the time of germination (Fig. 6, A ; Fig. 9, 2). 

 This food is called Perisperm (Gr. peri, around, sperma, 

 seed), because it asually obliterates the embryo-sac and fills 

 the cells of the nucleus, thus surrounding the embryo, which 

 is the soul of the seed. It is the perisperm in the grains — 

 Wheat, Oats, Maize, etc. — which furnishes our flour and 

 meal. [Sometimes the embryo-sac persists at a certain 



