CHAP. 11. OVULE. 181 



the base of the nucleus; and there it expands into a sort of 

 vascular disk, which is called the chalaza (Plate V. fig. 24. 

 f, 25. g). As the chalaza is uniformly at the base of the 

 nucleus, it will follow that, in Orthotropous and Campulitro- 

 pous ovules it is confounded with the hilum ; while it is only 

 distinguished in Anatropous ones, in which alone it is dis- 

 tinctly to be recognised. 



It has been remarked that the raphe or vascular extension 

 of the placenta always occupies the side next the ventral 

 suture of the ovary ; and that when, as in Euonpiius, it is 

 turned towards the dorsal suture, that circumstance arises 

 from an alteration in the position of the ovule subsequent to 

 its being fertilised. 



It has also been stated that the passage through the 

 primine and secundine is called the foramen ; or the exos- 

 tome, when speaking of that of the primine ; and the endos- 

 tome, in speaking of the secundine. Upon these Mirbel 

 remarks, — " These two orifices are at first very minute, but 

 they gradually enlarge ; and, when they have arrived at the 

 maximum of dilatation they can attain, they contract and 

 close up. This maximum of dilatation is so considerable in a 

 great number of species, in proportion to the size of the 

 ovule, that, to give an exact idea of it, I would compare it 

 not to a hole, as those express themselves who have hitherto 

 spoken of the exostome and endostome, but to the mouth of 

 a goblet or of a cup. It may therefore be easily understood, 

 that, to perceive either the secundine or the nucleus, it is not 

 necessary to have recourse to anatomy. I have often seen, 

 most distinctly, the primine and secundine forming two large 

 cups, one of which encompassed the other without entirely 

 covering it, and the nucleus extending itself in the form of 

 an elongated cone beyond the secundine, to the bottom of 

 which its base was fixed." 



In practical botany the detection of the foramen is often a 

 matter of great importance ; for it enables an observer to 

 judge from the ovule of the direction of the radicle of the 

 future embryo : it having been ascertained by many observ- 

 ations that the radicle of the embryo is almost always pointed 

 to the foramen. A partial exception to this law exists, how- 



N 3 



