342 ORGANOGRAPHY. 



teguments, as in Grasses, in which case it is described as external; 

 or it may he surrounded by the albumen on all sides, except on 

 its radicular extremity, as in the Pansy {fig. 755), when it is 

 internal. Sometimes the end of the radicle, as in the Coniferse, 

 becomes united to the albumen, and can no longer be distin- 

 guished. 



The embryo is said to be axile or axial when it has the same 

 direction as the axis of the seed, as in Heart's-ease {fig. 755); 

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

 {fig. 761). 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. 762), and in Lychnis {fig. 

 763), 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. 761). Some apptirent exceptions to these relative positions 

 occur in the Euphorbiacese, &c., but such are merely accidental 

 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 

 is thus seen to be generally constant, it must necessarily 

 happen from the varying relations which the hilum bears to the 

 micropyle and chalaza, that its relation to the radicle and 

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

 ner. Thus in an orthotropous seed, as Rumex {fig. 761), the 

 chalaza and hilum coincide with 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 

 anatropous seed, as Pansy {fig. 755), v/here 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 Jiomotropous. In 

 a campylotropous seed, where the chalaza and micropyle are 

 both near to the hilum, as in Lychnis {fig. 763), the two extremi- 

 ties 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. AVe have already described the 

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

 (see page 327), which we found might be either erect, suspended, 

 pendulous, ascending, or horizontal, in the same sense as pre- 

 viously mentioned when speaking of the ovule. The radicle is 

 said to be superior or ascending, as in the Nettle {fig. 760) and 



