HOW PLANTS GROW. 



vesicle never becomes anything more than a grain of soft pulp, unless the ovule 

 has been acted upon by the pollen. 



" 385. The pollen which falls upon the stigma, grows there in a peculiar way : 

 its delicate inner coat extends into a tube (the pollen-tube), which sinks into the 



loose tissue of the stigma 



Fig. 2. 



Fis. 3. 



Fig. 4. 



Fig. 5. 



Fig. 6. 



and the interior of the style, 

 something as the root of a 

 seedling sinks into the loose 

 soil, reaches the cavity of 

 the ovary, and at length 

 penetrates the orifices of an 

 ovule. The point of the 

 pollen-tube reaches the sur- 

 face of the embryo-sac, and 

 in some unexplained way 

 causes a particle of soft, 

 pulpy, or mucilaginous mat- 

 ter (Fig. 2) to form a mem- 

 branous coat, and to expand 

 into a vesicle, which is the 

 germ of the embryo. 



"386. This vesicle (shown 

 detached and more magnified 

 in Fig. 3) is a specimen of 

 what botanists call a cell. 

 Its wall of very delicate 

 membrane incloses a mucila- 



Fig. 7. Fig. 8. Fig. 9. 



Fi£r. 10. 



Fig. 2. — Magnified pistil of Buckwheat ; the ovary and ovule divided lengthwise : some pollen on the stigmas, 

 one grain distinctly showing its tube, which penetrates the style, reappears in the cavity of the ovary, enters 

 the mouth of the ovule (o), ami ri'aches the surface of the embryo-sac (.y), n^ar the embryonal vesicle (v). 



Fig. 3. — Vesicle or first cell of the embryo, with a portion of the summit of the embryo-sac, detached. 



Fig. 4. — Same, more advanced, divided into two cells. 



Fig. .l. — Same, a little further advanced, consisting of three cells. 



Fig. 6 — Same, still more advanced, consisting of a little mass of young cells. 



Fig. 7. — Forming embryo of Buckwheat, moderately magnified, showing a nick at the end where the cotyle- 

 dons are to Vie. 



Fig. 8. — Same, more advanced in growth. 



Fig. 9 — Same, still further advanced. . 



Fig. 10. — The completed embryo, displayed and straightened out ; the same as shown in a section when folded 

 together. 



ginous liquid, in which there are often some minute grains, and commonly a larger 



soft mass (called its nvclens). 



387. Growth takes place by this vesicle or cell, after enlarging to a certain 

 dividing by the formation of a cross partition into two such cells, cohering 



Vol. VII.— November, 1851. 



