VARYING RELATIONS OF THE PARTS OF THE EMBRYO. 347 
character is turned towards the micropyle (fig. 780, 7), in which 
case it is said to be homoblastic ; and the cotyledonary extremity 
is then directed to the chalaza, ch. Some apparent excepti ns 
to these relative positions occur in the Euphorbiacez, and a few 
other plants, when the radicle is described as enantioblastic ; 
but such are merely accidental deviations arising from certain 
trifling irregularities in the course of the development of the 
parts of the seed. 
Fic. 780.’ 
Fic. 779. 
Fig. 779. Vertical section of the fruit of the Nettle, containing a single 
seed. ¢. Integuments of the seed. pl. Placenta. 7. Radicle. sf. Stigma. 
Fig. 780. Vertical section of the fruit and solitary erect orthotropous 
seed of the Dock (Rumer). ov. Pericarp. mic. Micropyle. pl. Embryo 
which is inverted or antitropous, and turned towards one side of the albu- 
men, alb. ch. Chalaza. 7. Radicle. Fig. 781. Vertical section of the 
carpel of Mirabilis Jalapa, containing one seed. a. Pericarp. s. Style. 
e. Peripherical embryo with its radicle, 7, and cotyledons, c. p. Albu- 
men. ¢. Integuments of the seed. Fig. 782. Vertical section of the seed 
of Lychnis dioica. te. Integuments. emb. Embryo on the outside of the 
albumen, a/b, The embryo is amphitropous. 
While the relation of the radicle and cotyledonary portion is 
thus seen to be generally constant, it must necessarily happen 
from the varying relation which the hilum bears to the micro- 
pyle and chalaza, that its relation to the radicle and coty- 
ledonary portion of the embryo must also vary in like manner. 
Thus in an orthotropous seed, as Rumesw ( fig. 780), the chalaza 
and hilum coincide with each other, and the radicle is then 
turned towards the apex of the seed, and the cotyledonary 
portion to the chalaza and hilum ; in this case the embryo is 
said to be antitropous or inverted (figs. 731 and 780). In an 
anatropous seed, as Heartsease (fig. 774), where the micropyle 
is contiguous to the hilum, h, and the chalaza, ch, at the 
opposite extremity, the radicle, 7, will point towards the hilum 
or base of the seed, and then the embryo is said to be erect or 
homotropous. In a campylotropous seed, where the chalaza and 
micropyle are both near to the hilum, as in Lychnis (fig. 782), 
