112 



OEGANOGEAPHY AND GLOSSOLOGY. 



parts of which it is composed, it must be cut vertically, when it usually discloses an 

 elongated axis with a small protuberance marked with an oblique or vertical fissure ; 

 this protuberance represents the plumule ; the fissure through which the two first 

 leaves will appear marks the separation between the caiilicle aud cotyledon. 

 Owing to the small size of the parts, it is sometimes difiicult to distinguish the 

 cotyledonary from the radicular end ; but the latter, which answers to the micropyle, 

 is usually nearer to the integument than the former ; this is evident in the seed of 

 Arum (fig. 639). In Oats and other Graminece (fig. 640), the 

 seed, if halved longitudinally along the furrow on its inner 

 face, discloses a very abundant farinaceous parenchyma (a), 

 of which we shall presently speak ; from the base of the seed 

 along its dorsal face rises the embryo (e, a, c), of a yellow, semi- 

 transparent colour; within this is a fl.eshy leaf (c), which 

 extends one-third of the length of the seed ; this leaf encloses 

 several others, successively smaller (g), which enfold each 

 other, and are placed between the largest leaf (o) 

 and the dorsal face of the ovary (o) ; all rise from 



639. Arum. 



Seed out 



vertically (mag,). 



641. Oat. 



Isolated embryo seen on 



its outer face (mag.j. 



643. Aconite. 



Seed cut 



Vei-tically (mag.). 



640. Oat. 



Vertical section of 



fruit (mag.). 



642. Oat. 



Germinating embryo. 



(mag.). 



an enlarged neck which narrows towards the base into an obtuse cone ; the interior 

 leaf (c) is the cotyledon, the others (g) form the plumule, the conical disk is the 

 caulicle, terminated by the radicular end (e). 



If we extract the entire embryo (fig. 641), we perceive the cotyledon, which is 

 large, and hollowed into a sort of spoon-shape, in the middle of which lies the 

 plumule, forming a closed bag ; in the middle of this bag is a very small longitudinal 

 slit, which enlarges later into a sheath, to open a passage for the contained leaves ; 

 below is the caulicle, bearing the cotyledon on its side, and the plumule in its axis ; 

 its free end is terminated by rounded protuberances, in which holes will form, 

 whence radicular fibres will emerge at the period of germination, as from so many 

 sheaths (fig. 642, Col.). 



Albumen. — Many seeds contain, besides the embryo, a disconnected accessory 

 mass of parenchyma, named albumen {albumen, perisperTmim), the formation of 

 which will be explained in the chapter on the Ovule. It is destined to nourish the 

 embryo, and exists at an early period in all seeds ; if only a portion of it is absorbed 

 by the embryo, the rest hardens, up to the period of germination, and the embryo is 

 said to be albuminous (e. albuminosus) ; if it be absorbed, the embryo is exalbuminous 



