284 



THE FLOWER. 



604 



605 



607 



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

 the part reached by the pollen-tube. Not rarely it adheres to the 

 eoo eoi 602 cos wa ll of the sac exactly 



opposite the termination 

 of the pollen-tul ie. This 

 is called the embryonal 

 vesicle. To it the con- 

 tents of the pollen-tube 

 arc in some manner tran 

 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 sitspensor or pro- 

 I'nihryo). The terminal cell of this divides again and again in 

 three directions, producing a mass of cells which shapes itself 



into the embryo, the initial 

 plant of a new genera- 

 tion. Ordinarily the sus- 

 pensor soon disappears. 

 It is attached to the ra- 

 dicular end of the em- 

 bryo, which consequently always points to the foramen or 

 microp3'le of the seed. The process in Gymnosperms is more 

 complex, and has to be separately described. 



533. Polyembryony, the production of two or more embryos 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, Santahnn, &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 adventive 

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

 sac and wholly independent of fertilization. 1 Two kinds of 



1 Strnslmrger, TYlier Polyembryonie, in Xritschr. Xntunvis. Jena, xii. 

 1878 (see Anicr. Jour. Sri. April, 1870). 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 af its extremity. 600. 

 The same, with the embryo a litlle more developed. G01. Tlie same, more developed 

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

 cotyledons more manifest. i;n:;. The embryo nearly completed. 



FIG f.04-fiOr>. Formiiiiremliryo from a half-grown seed of Buckwheat, in three stages. 

 607. Same, with the cotyledons fully developed. 



