OEGANS OF REPRODUCTION. 351 



direction as the axis of the seed, as in Heart's-ease {fig. 752); 

 when this is not the case, it is abaxile or eccentric, as in Rumex 

 (fig. 758). In the latter case, the embryo is frequently alto- 

 gether on the outside of the albumen, and directly below the in- 

 teguments, as in Mirabilis Jalapa {fig. 759), and in Lychnis 

 {fig. 760), in which case it is described as peripherical. 



We have already observed, that the radicle is turned towards 

 the micropyle, and the cotyledonary extremity to the chalaza 

 {fig. 752). Some apparent exceptions to these relative posi- 

 tions occur in the Euphorbiacese, &c., but these are merely ac- 

 cidental deviations, arising from certain trifling irregularities in 

 the course of the development of the parts of the seed. 



While the relation of the radicle and cotyledonary portion are 

 thus seen to be generally constant, it must necessarily happen 

 from the varying relations which the hilum bears to the micro- 

 pyle and chalaza, that the relation of that body to the radicle and 

 cotyledonary portion of the embryo must also vary in like man- 

 ner. Thus in an orthotropous seed, as Rumex {fig. 758), the 

 chalaza and hilum coincide witli each other, and the radicle is then 

 turned towards the apex of the seed or to the micropyle, and 

 the cotyledonary portion to the chalaza and hilum; in this case 

 the embryo is said to be antitropous or inverted. In an anatro- 

 pous seed, as Pansy, {fig. 752), where the micropyle is con- 

 tiguous to the hilum, and the chalaza at the opposite extremity, 

 the radicle will point towards the hilum or base of the seed, 

 in which case the embryo is said to be erect or homotropous, as 

 the radicle is considered the base of the embryo, and the 

 chalaza its apex. In a campylotropous seed, where the chalaza 

 and micropyle are both near to the hilum, as in Lychnis {fig. 

 760), the two extremities of the embryo, which in such cases is 

 generally peripherical, become also approximated, and it is said 

 to be amphitropous. Thus when we wish to know the direction 

 of the embryo, by ascertaining the position of the hilum, chalaza, 

 and micropyle, it is at once evident. 



We have now only to explain the different terms which are 

 in use, to express the relations which the embryo bears to the 

 cavity or cell in which it is placed. We have already described 

 the terms used in defining the position of the seed to the same 

 cavity, which we found might be either erect, suspended, pen- 

 dulous, ascending, or horizontal, in the same sense as previously 

 mentioned when speaking of the ovule. The radicle is said to 

 be superior or ascending, as in the Nettle {fig. 757) and Rumex 

 {fig. 758), when it is directed towards the apex of the pericarp; 

 inferior or descending when it points to the base ; centripetal 

 if turned towards the axis or centre of the pericarp; and centri- 

 fugal if towards the sides. The above relations of the embryo 

 to the other parts of the seed, and to the pericai'p, are sometimes 

 of great practical importance. 



