FUNDAMENTAL OEGANS. 



137 



will be straight, as in the Nettle, but the . chalaza will be the antipodes of the 

 hilum, the micropyle nearly touching the latter, and the radicle corresponding to 

 the base of the ovule ; such an embryo is called homotropous (ov. homotropus). 

 There are many examples of this (Sage, fig. 579 ; Chicory, fig. 580). 



2. When the hilum and chalaza (figs. 724 ch, 725) are inseparable, and one 

 side of the primine (p) is more developed 

 than the opposite side, the one lengthens while 

 the other remains stationary ; the resistance 

 of the stationary side causes the lengthening 

 side to turn around the centre of resistance ; 

 the ovule (n) thus bent back upon itself is said 

 to be campylotropous (ov. campylotropum) . 

 Here the embryo will follow the curvature of 

 the ovule, and the micropyle and chalaza (ch) 

 being both close to the hilum, the radicle and cotyledonary ends will be only 

 separated by the hilum, and the embryo is called amphitropous. The Wallflower (figs. 

 724, 725) and the Mallow (figs. 726-730) are well-marked instances of the curved 

 ovule and amphitropous embryo. 



To these three types (orthotropous, anatropous, and campylotropous) all ovules 

 properly belong ; but there are many cases of intermediate types, which it is neces- 

 sary to take into account. In one case which, although very rare, runs through 

 the whole family of Primulacece, and occurs in Vinca, one side of the ovule develops 



724. "Wallflower. 



Campylotropous ovule 



(mag.). 



725. Wallflower. 



Campylotropous ovule, cut 



vertically (mag.). 



726. 727. 728. 729. 



Mallow. Campylotropous ovule in various stages of development (mag.). 



730. Vertical section 

 of fig. 729. 



enormously, while the other gradually atrophies ; this action continues after 

 fertilization, and the micropj^le, approaching the hilum more and more, ceases to 

 correspond to the radicle, which may hence be variable in direction ; most commonly 

 the axis of the embryo becomes parallel to the hilum, and the embryo is called 

 heterotropous (ov. heterotropus, Plantain, fig. 592 ; Asparagus, fig. 594). 



When the seed is mature, it becomes difficult to distinguish in its coats (testa 

 and endopleura) the primine, secundine, tercine (nucleus), and quintine (embry- 

 onic sac), which all enter into its composition. The testa evidently represents 

 the primine ; and, as the raphe has pursued its course between it and the secundine, 

 this latter must be represented by the endopleura ; but the nucleus and embryonic sac 

 are either pushed back by the embryo, and reduced to membranes lining the inner wall 

 of the secundine, or they completely disappear; the secundine itself may indeed disap- 

 pear, and the embryonic sac alone remain with or without the nucleus. Lastly, these 



