226 



ESSENTIAL ORGANS. THE OVULE. 



418,1 



418,2 



418,3 



latter names are in the present day used by botanists as denominating 

 the outer and inner covering, witho u t reference to their order of 



development. At the apex 

 of the nucleus these integu- 

 ments leave an opening or 

 foramen composed of two 

 apertures; that in the pri- 

 mine (fig. 418, 3, ex), called 

 exostome (i%a, outside, and 

 tnof^a., mouth), that in the 

 secundine (fig. 418, 3, e,d\ 

 endostome (st/^ov, within). The 

 foramen of the ovule is also called micropyle (^/xg&r, small, and vfa-n, a 

 gate) ; but this name is often restricted to its appearance in the seed after 

 fecundation. The length of the canal of the foramen depends on the 

 development of the nucleus, as well as the thickness of the integuments. 

 The embryo-sac is sometimes prolonged beyond the apex of the nucleus, 

 as noticed by Meyen in Phaseolus and Alsine media, and by Griffith in 

 Santalum album and Loranthus. Some authors, as Mirbel, consider 

 the ovule in reference to the embryo, and speak of five coverings of 

 the latter, viz., 1. primine ; 2. secundine ; 3. tercine, or the nucleus ; 

 4. quartine, a temporary cellular layer, which is occasionally formed 

 at an after period around 5. quintine, or the embryo-sac. By most 

 botanists the nucleus and sac with its two integuments, are mentioned 

 as the ordinary structure of the ovule. 



465. All these parts are originally cellular. The nucleus and in- 

 teguments are united at the base of the ovule by a cellulo-vascular 

 membrane, called the chalaza (fig. 421 ch). This is often coloured, of 

 a denser texture than the surrounding tissue, and is traversed by fibro- 

 vascular bundles, which come from the placenta, in order to nourish 

 the ovule. The hilum indicates the organic base of the ovule, while the 

 foramen marks its apex. When the ovule is so developed that the 

 union between the primine, secundine, and nucleus with the chalaza, 

 is at the hilum or base (next the placenta), and the foramen is at the 

 opposite extremity (figs. 417, 418), the ovule is orihotropal, orthotro- 

 pous or atropous (6^60;, straight, and rjoVo?, mode, or , privative, and 

 Tf7T6), I turn). This is the state of an ovule when it first makes its 

 appearance, and occasionally, as in Polygonacese, it remains permanent. 

 In such ovules, a straight fine drawn from the hilum to the foramen 

 passes through their axes. 



