342- THE STRUCTURE OF ECONOMIC PLANTS 



ANATOMY 



The Seed. — The mature seeds are large and globular with a 

 thin seed coat which encloses an embryo consisting of two fleshy, 

 hemispherical cotyledons, a well-developed hypocotyl, and an 

 epicotyl with the first foliage leaves, or trifid bracts, already 

 differentiated. The seeds vary greatly with respect to color, 

 degree of smoothness, and the character of the reserve foods con- 

 tained in the cotyledons. 



The structural details have been described by Pammel (2.^), 

 Winton (34), Tschirch and Oesterle (^8); and other investigators 



--73 ep 



- cot 



s ep 



Fig. 174. A, section through seed coat and portion of cotyledon; B, section through seed 

 coat in region of hilum ; C, enlarged detail of porous sclerenchyma beneath hilum : cot, coty- 

 ledon; cot ep, cotyledonary epidermis; hi, hilum; par, parenchyma; p ep, palisaded epi- 

 dermis of seed coat ; p epi and p ep-i, double layer of palisaded epidermis surrounding hilum ; 

 scl, porous sclerenchyma; s ep, subepidermal cells which are more extensive beneath hilum, 

 forming cushion in which sclerenchyma cells are embedded. (^ and C, redrawn from 

 Tschirch and Oesterle, Anatomtscher Atlas der Pharmakognosie und Nahrungsmittelkunde , Herm. 

 Tauchnitz; B, redrawn from Winton and Winton, Structure and Composition of Foods, John 

 Wiley and Sons, Inc.) 



have added more or less complete accounts in connection with 

 studies of germination, food storage, and related subjects. In 

 the mature seed, the coat is thin and somewhat brittle, except at 

 the hilum, consisting of three layers, two of which are but one cell 

 in thickness while the third may be several cells thick. (Fig. 174, 

 y4.) All the layers are a part of the outer integument, since the 

 inner integument is completely resorbed within three or four days 

 after fertilization. 



