293 



THE FLOWER. 



coat : this appears as a circular ring around the base of the forming 

 nucleus, which gradually becomes cup-shaped, and at lenglh covers 

 it like a sac, remaining open, however, at the summit. This 



orifice is called the Foramen, 

 or Micropyle. In far the 

 greater number of cases, a 

 second envelope is formed out- 

 side of the first, beginning in 

 the same way, though always 

 later than the inner one, which, 

 however, it eventually over- 

 takes and encloses. Mirbel 

 named the exterior coat of the 

 ovule the Primine, and the in- 

 terior the Secundine, — names which are attended with the objec- 

 tion that the secundine or inner coat is actually older than the 

 primine or exterior coat. Both sacs are open at the apex, and the 

 summit of the nucleus points directly towards the apertures. The 

 orifice or foramen of the primine or exterior integument is called 

 the Exostome (or outer orifice) ; that of the interior or secundine, 

 the Endostome (or inner orifice). The coats of the ovule and 

 the nucleus are distinct and unconnected, except at the base, or point 

 of attachment to the funiculus, where they are all confluent : this 

 point of union receives the name of the Chalaza (Fig. 521, d). 

 Through the funiculus and chalaza the ovule derives its nourish- 

 ment from the placenta ; through the opening at the summit, the 

 nucleus receives the tubular prolongation of the pollen, which incites 

 the formation of the embryo. 



5G5. Ovules occur under four principal forms, viz. the orthotro- 

 pous or straight, the campylotropous or curved, the amphltropous or 

 half-inverted, and the anatropous or inverted. The simplest, al- 

 though the least common of these, is 



506. The Ol'tllOtropoilS Ovule, also termed atropous (viz. not turned). 

 It is the form which this organ assumes in the Buckwheat family 

 (Fig. 518), and several others, and is likewise shown in Fig. 520, 

 52G, and a longitudinal section of it in Fig. 521. Here no change in 



FIG. 520. An orthotropous ovule 521. Longitudinal section of the same, more magnified : 

 a, the primine; b, the seeundine; c, the nucleus; d, the chalaza 522 An amphitropous 

 ovule 523 Three anatropous ovules, with long funiculi, attached to a portion of the placenta. 

 524 One of the same, more highly magnified, exhibiting its cellular structure. 525. A cainp'y- 

 lotropous ovule. 



