228 ESSKNTIAL ORGAXS. THE OVULE. 



to the hilum (fig. 421, 5, h) and the chalaza is also earned round so 

 as to be at the opposite extremity (fig. 421, 5, c), then the ovule 

 becomes inverted, anatropal or anatropous (d,va,-r^a, I subvert). 

 In this case (fig. 422), the union of the chalaza, ck, with the nucleus, 

 n, is removed from the hilum, and the connection 

 between the chalaza and placenta is kept up by a vas- 

 cular cord, r, passing through the funiculus, and called 

 the raphe (ZK<PYI, a line). The raphe often forms u 

 ridge along one side of the ovule, and it is usually 

 on the side of the ovule next the placenta. Some 

 look upon this kind of ovule as formed by an elongated 

 funiculus (fig. 421, 5, /) folded along the side of the 

 ovule, and becoming adherent to it compeletely ; and 

 support this view by the case of semi-anatropal ovules, 

 where the funiculus is only, as it were, partially 

 attached along one side, becoming free in the middle; and also by cases 

 where an anatropal ovule, by the separation of the funiculus from its 

 side, becomes an orthotropal seed. 



468. The anatropous form of the ovule is of very common occurrence, 

 and may probably aid in the process of fertilization. Ovules which are 

 at first orthotropous, as in Chelidonium majus (fig. 421, 2), become 

 often anatropous in the progress of development (fig. 421, 4). When 

 the ovule is attached to the placenta, so that the hilum is in the middle, 

 and the foramen and chalaza at opposite ends, it becomes transverse, 

 amphitropal or heterotropal (dp,}, around, erhof, diverse). 



469. The nucleus of the ovule becomes hollowed at a particular part 

 (fig. 415 c), so as to form a cavity. Mirbel states that the whole nucleus 

 is transformed into a membrane called the tercine, lining the secundine, 

 and that in its interior another covering, the quartine, and finally, the 

 embryo-sac, are produced. The view, however, generally adopted, is 

 that the embryo-sac is formed within the nucleus, assuming a greater 

 or less size according to circumstances, and in some instances reducing 

 the nucleus to a mere external sac. In the interior of the embryo- 

 sac, cellular layers are deposited from without inwards, the earlier 

 ones probably forming the fugacious quartine of Mirbel. 



470. In the Misletoe there are two or three embryo-sacs. The neck 

 of the embryo-sac in Veronica and Euphrasia becomes elongated and 

 swollen, and from it are developed certain cellular or filamentous 

 appendages, which are probably connected with the nutrition of the 

 embryo. 



471. The position of the ovule relative to the ovary varies. When 

 there is a single ovule, it may be attached to the placenta at the base 

 of the ovary (basal placenta), following a straight direction, and being 



Fig 122. Anatropous ovule of Dandelion, cut vertically, ch, Chalaza. r, Raplie. , Nucleus. 



