ESSENTIAL OEGANS — THE OVULE. 



255 



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

 called the chalaza (fig. 458 ch). This is often coloured, of a denser 

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

 vasoular bundles, which come from the placenta, to nourish the ovule. 

 When the ovule is so developed that the union between the primine, 

 seoundine, and nucleus, with the chalaza, is at the hilum or base (next 

 the placenta), and the foramen is at the opposite extremity (figs. 453, 

 454), the ovule is orthotropal, m-tlwtropous, or atropous (ogdl>g, straight, 

 and Tgomg, mode ; or u,, privative, and rfiTru, I turn). This is the 

 position of an ovule when it first makes its appearance, and occasion- 

 ally, as in Polygonacese, it remains as the permanent condition. In 

 such an ovule a straight line drawn from the hilum to the foramen 

 passes along the axis of the ovule. 



In general, however, changes take place in the ovule, so that it 

 assumes a different form. Thus it may be curved upon itself, so that 

 the foramen approaches the hilum or placenta, and ultimately is placed 

 close to it, while the chalaza is only slightly removed from the hUum. 

 This change depends apparently on the ovule increasing more on one 

 side than on the other, and as it were drawing the chalaza slightly to 

 the side of the hUum opposite to that to which the foramen is' inclined. 



IC^ 



Fig. 465. 



Fig. 466. 



Such ovules are called campylotropal or campyhtropous (xa/friiXof, 

 curved), when the portions on either side of the line of curvation are 

 unequal (fig. 455) ; or camptotropal (xa/^vrrbg, curved), when they are 

 equal (fig. 456). Curved ovules are found in Leguminosse, Cruciferse, 

 and Caryophyllacese. The union between the parts of the curved 

 portion usually becomes complete, but in some cases there is no union, 

 and the ovules are licotropal, or horse-shoe shaped (Xsxos, a hollow disk, 

 and rjoVos, mode or form). 



Pig. 465. Campylotropal or Campylotropua ovule of the Stock. 1, Ovule eutire. 2, Ovule 

 cut lengthwise. /, Faniculus or umbilical cord, c, Chalaza. *, Nucleus, te, Primine or 

 outer covering. (^, Secundine or inner covering, ex, Exostorae. ed, Endostome. Fig. 456. 

 Carpel of Menispennum canadense, with a curved or camptotropal ovule, o. /, Funiculus. 

 s. The base of the style. 



