276 



MANUAL OP BOTANY 



are folded in opposite directions, and become equitant or 06- 

 volute ; sometimes other still more complicated arrangements 

 occur. 



The position of the radicle in relation to the cotyledons is 

 also liable to much variation. The radicle may follow the 

 same direction as the cotyledons, or a different one. In the 

 former case, if the embryo is straight, the radicle is more 

 or less continuous in a straight line with the cotyledons, as in 

 the Pansy {fig. 600, r) ; if, on the contrary, the embryo is 

 curved, the radicle is curved also (fig. 601), and sometimes 

 the curvature is so great that a spiral is formed, as in Bunias 

 (fig. 602). In the latter case, where the direction of the coty- 

 ledons and radicle is different, the latter may form an acute, 

 obtuse, or right angle to them ; or be folded back to such an 



Fig. 600. 



Fig. 601. 



Fig. 602. 



Fut. 600. Tevtical section of the seed of the Pansy or Heartsease, h. Hilum. 

 pj. Embryo with its radicle, r, and cotyledons, co. ch. Ohalaza. al. 



Albumen, ra. Uaphe. The embryo is erect or homotropous. Fig. 601. 



Vertical section of the seed of the Poppy, with the embryo slightly 



onrved in the axis of albamen. Fig. 602. Vertical section of the seed of 



Bunias, showing its spiral embryo. 



extent as to lie parallel to the cotyledons, in which case the 

 radicle may be either applied to their margins, as in the Wall- 

 flower (fig. 604, r), when the cotyledons are said to be accumbent ; 

 or against the back of one of them, as in Isatis (fig. 603, r), when 

 they are termed incumbent. 



Belation of the Embryo to the other Parts of the Seed, and to 

 the Fruit. — It must necessarily happen that when the albumen 

 is present, the size of the embryo is in inverse proportion 

 to it ; thus in Grasses (Jig. 591) we have a large deposit of 

 albumen and but a small embryo, while in the Nettle (fig. 

 605) the embryo is large and the albumen very small. The 

 embryo may be either external to the albumen (figs. 591 and 

 608), and thus in contact with the integuments, as in Grasses, 

 in whioh case it is described as external ; or it may be 

 surrounded by the albumen on all sides, except on its radicular 



