MORPHOLOGY OF AxXGiOSPERMS. 



153 



The terms used in describing tlie kinds of ovules (atropous, 

 anatropous, campylotropous, etc.), are retained in the description 

 of the seeds ; and in describing the different.parts of the seed some 

 of the terms which were apphed to the ovule are also retained, as 

 chalaza and raphe : the seed when ripe usually becomes detached 

 from its stalk and the resulting scar is called the iiilum ; that 

 part of the seed corresponding to the foramen of the ovule is 

 more or less closed and is known as the micropyle; the embryo 



Fig. 92. Rhamnus cathartica. A. cross-section through wall of the pericarp. E. epi- 

 carp; F, sarcocarp; H, endocarp; e, epidermis; o, calcium oxalate in cells of hypodermis; p 

 parenchyma; h, secretion cells containing a substance which is insoluble in alcohol or chloral 

 solutions, soluble in solutions of potassium hydroxide, and colored reddish brown or green- 

 ish with ferric chloride solutions; c, calcium oxalate cells of endocarp; w, sclerotic cells; f, 

 stereome cells. B, cross-section of entire fruit, showing one seed; E, F. H, g, f, w, as in A; 

 S, seed-coat; S', outer wall of seed-coat; End, endosperm; c, cotyledons; g, vascular bundle. 

 C, cross-section of a seed: S^, S-, S^, different layers of the seed-coat: R, vascular bundle of 

 raphe; t, position of vessels of mestome strand; g, mestome strand; Rf. cleft in which raphe 

 is situated; End, endosperm; C cotyledons: Sv, cells with thick walls; Sp, parcnchymatic 

 cells. After Mever. 



develops in such a way that the tip of the young root always 

 points in the direction of the micropyle. 



In the fully developed embryo three distinct parts may be dif- 



