OSGANS OF REPRODUCTION. 



333 



Fig. 719. Orthotropous ovule of Polygonum, ch. Cha- 

 laza. x>'rim. Primine. sec. Secundine. n. Nucleus. 



s. Embryo-sac. m Micropyle r-Fig. 720. Campy- 



lotropous ovule of AVallflower. /. Funiculus, ch. 

 Clialaza. p. Primine. s. Secundine. n. iJJucleus. 

 mic. Micropyle. 



or atropoiis. In such an ovule therefore, the micropyle, m, 

 would be situated at the geometrical apex, or at the end 

 farthest removed j'l 719. Fig. 720. 



from the hilum, 

 and the organic 

 and geometrical 

 apices would con- 

 sequently corre- 

 spond; while the 

 chalaza,c/j, would 

 be situated at the 

 base of the ovule 

 or hilum. 



It generally hap- 

 pens that the 

 ovule instead of 

 being straight as 

 in the above in- 

 stance, becomes 

 more or less 

 curved, or even altogether inverted. Thus in the "Wallflower 

 (Jig. 720), and other plants, of the order to which it belongs, 

 as well as in the Caryophyllacefe, &c., the apex of the 

 o^Tile, becomes gradually turned downwards towards the base, 

 and is ultimately placed close to it, so that the whole ovule is bent 

 upon itself, and a line drawn from the micropyle, mic, through 

 the axes of the nucleus, n, and its coats would describe a curve ; 

 hence such ovules are called campylotropons or curved. In these 

 ovules, the chalaza, ch, and hilum correspond as in ortho- 

 tropous ones, but the micropyle, mic, instead of being at the 

 geometrical apex of the o^Tile, is brought down close to the 

 hilum or base. The progressive development of the campylo- 

 tropons o^'ule is well seen in the ]\Iallow, as represented in fig. 

 722. This kind of ovule appears to be formed by one side 

 developing more extensively than the other, by Avhich the micro- 

 pyle is pushed round to the base. 



In a third class of ovules the relative position of parts is 

 exactly the reverse of that of orthotropous ones — hence such 

 are called anatropous or inverted ovules. This arises from an 

 excessive development of the coats of the ovule on one side, by 

 which the chalaza {fig. 721, cli) is removed from the hilum, h, or 

 placenta, to the geometrical apex of the ovule; the micropyle,/, 

 is at the same time turned towards the hilum, h. The gradual 

 development of an anatropous ovule may be well seen in the 

 Chelidonium. In anatropous ovules, a connexion is always 

 maintained between the chalaza and the hilum or placenta, by 

 means of a vascular cord or ridge, called the raphe (fig. 721, r), 

 which is generally considered as an elongated funiculus adhe- 



