324 



ORGANOGRAPHY. 



its coats and nucleus, called the chalaza, is at the base or hilum, 

 close to the placenta or funiculus ; in which case, a straight line 

 would pass from the micropyle through the axes of the nucleus 

 and its coats to the hilum. In rare instances this relation of parts 

 is preserved throughout its development, as in the Polygonaceae 

 {fig. 722); in which case the ovule is termed orthotropous or 

 atropous. In such an ovule therefore, the micropyle, m, would 

 be situated at its geometrical apex, or at the end farthest removed 



Fig. 722. 



Fig. 723. 



from the hilum, 

 and the organic 

 and geometrical 

 apices would con- 

 sequently corre- 

 spond ; while the 

 chalaza, ch, would 

 be situated at the 

 base of the ovule 

 or hilum. 



It generally hap- 

 pens, however,that 

 the ovule instead 



Fig. 722. Vertical section of an orthotropous ovule of *^* being straight 

 Polygonum, ch. Chalaza. prim. Primiiie. sec. Se- as in the above 

 cundine. 7i. Nucleus, s. Embryo-sac. '«• Micropyle. -^ Vippatyipc 



Fig. 723. Vertical section of a canipylotropous in=>i'i'"Le, uecumeb 



ovule of Wallflower. /.Funiculus, c/i. Clialaza. }>. more or lesS 

 Primine. s.-Socundine. n. Nucleus, mic. Micropyle. (,^j.Ygf| qj. gygjj qI_ 



together inverted. Thus in the Wallflower (fig. 723), and other 

 plants, of the order to which it belongs, as well as in the Caryo- 

 phyllaceae, &c., the apex of the ovule 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, 7mc, through the axes of the nucleus, n, and 

 its coats would describe a curve ; hence such ovules are called 

 cam'pylotro'pous or curved. In these ovules, the chalaza, ch, and 

 hilum correspond as in orthotropous ones, but the micropyle, mic, 

 instead of being at the geometrical apex of the ovule, is brought 

 down close to the hilum or base. The progressive development 

 of the campylotropous ovule is well seen in the Mallow, as repre- 

 sented in fig. 725, a, b, c, d. This kind of ovule appears to be 

 formed by one side developing more extensively than the other, 

 by which the micropyle is pushed round to the base. 



In a third class of ov^iles the relative position of parts is 

 exactly the reverse of that of orthotropous ones — hence such 

 are called anatrojpous or inverted ovules. This arises from an 

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

 which the chalaza {fig. 724, ch) is removed from the hilum, h, to 

 the geometrical apex of the ovule ; the micropyle, /, is at the 

 same time turned towards the hilum, h. The gradual develop- 



