284 



THE FLOWER. 



of fertilization is found at the apex of the sac, at or adjacent to 

 the part reached b}' the pollen-tube. Not rarely it adheres to the 



wall of the sac exactly 

 opposite the termination 

 of the pollen-tube. This 

 is called the embryonal 

 vesicle. To it the con- 

 tents of the pollen-tube 

 are in some manner trans- 

 ferred. Upon which it 

 takes a more definite 

 shape, acquires a wall of 

 cellulose, and so becomes 

 a vegetable cell. This 

 divides into two, the lower 

 again into two, and so on, forming a chain (the suspensor or pro- 

 embryo) . The terminal cell of this divides again and again in 

 three directions, producing a mass of cells which shapes itself 

 GOG 607 into the embiyo. the initial 



a/1 f\ y^v/1 plant of a new genera- 



^ s t * on> Ordinarily the sus- 



pensor soon disappears. 

 ^ i >s Httacht'd to the ra- 

 dicular end of the em- 

 bryo, which consequently alwa}'s points to the foramen or 

 micropyle of the seed. The process in Gymnosperms is more 

 complex, and has to be separately described. 



533. Polyeinbryony ', the production of two or more emb^os in 

 one seed, is not uncommon in Gymnosperms (there being a kind 

 of provision for it), and is of occasional but abnormal occurrence 

 in Angiosperms, in the seed of Mistletoe, Santalum, &c. In 

 these it results from the production and fertilization of more 

 than one embryonal vesicle. Strasburger has recently ascer- 

 tained that the commoner polyembryony in the seeds of Onions, 

 Oranges, Funkia, &c., results from the production of adventlve 

 embryos, which originate in the nucleus outside of the embryo- 

 sac and wholly independent of fertilization. 1 Two kinds of 



1 Strasburser, Ueber Polyembryonie, in Zeitschr. Natunvis. Jena, xii. 

 1878 (see Amer. Jour. Sci. April, 1879). It was found that when, by exclu- 

 sion of pollen, the formation of a normal embryo was prevented, no adventive 



FIG. 599. Diagram of the suspensor and incipient embryo at its extremity. 600. 

 The same, with the embryo a little more developed. G01. The same, more developed 

 still, the cotyledons faintly indicated at the lower end. 602. Same, with the incipient 

 cotyledons more manifest. 603. The embryo nearly completed. 



FIG 604-600. Forming embryo from a half-grown seed of Buckwheat, in three stages. 

 607. Same, with the cotyledons fully developed. 



