70 



STKUCTURAL BOTANY. 



[58, 69. 



175. The aril is an occasional appendage, partially or wholly investing 

 the seed. It originates after fertilization, at or near the hilum, where the 

 seed is attached to its stalk (funiculus). Pine examples are seen in the gashed 

 covering of the Nutmeg, called mace, and in the scarlet coat of the seed of 

 Staff -tree. In the seed of Poly gala, etc., it is but a small scale, entire or 

 2-cleft, called caruncle. 



176. The position of the seed in the pericarp is, like that of the ovule, 

 erect, ascending, pendulous, etc. ( 149). Likewise, in respect to its inversions, it 

 is orthdtropous, andtropous, amphitropous, and campyldtrapom ( 141), terms already 

 denned. The anatropous is by far the most common condition. 



177. The hilum is the scar or mark left in the 

 testa of the seed, by its separation from the funiculus. 

 It is commonly called the eye, as in the Bean. In 

 orth6tropous and campy!6tropous seeds, the hilum cor- 

 responds with the chalaza ( 140). In other conditions 

 it does not; and the raphe ( 141) extends between 

 the two points, as in the ovules. The foramen of the 

 ovule is closed up in the seed, leaving a slight mark 



the micropyle. 



212 213 



208 210 ' 211 



202, Seed of Water Lily (Nymphaea), enlarged section ; alb., albumen ; a, the embryo contained, in the 

 embryo-sac ; s, tegmen ; p, testa ; r, raphe ; a", aril ; m, orifice ; /, funiculus. 203, Seed of Bean. 204, 

 Same, one cotyledon with the leafy embryo. 205, Seed of Apple. 206, One cotyledon showing the raphe 

 and embryo. 207, Fruit of Mirabilis ; embryo coiled into a ring. 208, Onion ; embryo coiled. 209, Con- 

 volvulus ; leafy embryo folded. 210, Embryo of Cuscuta. 211, Typha. 212, Ranunculus. 2i3, Hop. 



178. The seed-kernel may consist of two parts, the 

 embryo and albumen, or of the embryo only. In the 

 former case the seeds are albuminous; in the latter, 

 exalbuminous ; a distinction of great importance in 

 systematic botany. 



