300 



FERTrl-IZATION. 



the ovule or the seed as to be externally undistinguishable. The 

 seeds of Magnolia offer good illustrations of this. The mode of 

 formation and the internal structure of anatropous or inverted ovules 

 will be apparent on inspection of Fig. 530-536. 



569. The Amphitropons Ovule (Fig. 522, 528), also called heterotro- 

 pous, differs from the anatropous in having a short rhaphe (Fig. 

 528, r), extending from the chalaza (c) only about half-way to the 

 orifice (/"). It is attached accordingly by the middle of one side, 

 and has the chalaza at one end and the orifice at the other. It may 

 be regarded as a half-anatropous or half-inverted ovule ; and all gra- 

 dations occur between this and the anatropous form, into which it 

 would pass by the cohesion of the side of the ovule with the support 

 a little farther down. Amphitropons ovules are general in the Mal- 

 low and the Primrose families. As such an ovule stands with its 

 axis at right angles with the funiculus, if there be any, it is also said 

 to be transverse. 



570. Most of these terms apply to seeds as well as to ovules ; and 

 the general structure of the seed may be known beforehand from 

 that of the ovules. We are now prepared to contemplate the pro- 

 cess by which an ovule becomes a seed. 



Sect. IX. Fertilization akd Formation of the E^ibrto. 



571. In order to the formation of the embryo (118), the ovules 

 require to be fertilized by the pollen. Cases of parthenogenesis, 

 i. e. of the formation of perfect seed without the agency of pollen, 

 doubtless do sometimes occur, and have been noted in several 



FIG. 531. A similar side-view of the ovule of the last, a week or two later, and more mag- 

 nified ; showing the nucleus encircled by the coats in formation, as two rings or shallow cups 

 one within the other. 532 The same, a few days later, more advanced and beginning to turn. 

 533. The same, further advanced. 534. The same, soon after, with the inversion almost 

 complete, and the outer coat covering the inner, except at the orifice. 535. The completed 

 anatropous o\'ule rom a full-grown flower-bud. 536. A longitudinal section of the same, 

 displaying the rhaphe, the two coats, and the nucleus. 



