THE STRUCTURE OF SEEDS 39 



2. Kernel. 



Embryo (miniature plant, always present). 



(1) Cotyledons (seed leaves) 

 Development. 



(a) Leaf-like (squash). 



(b) Store food, but come up (bean). 



(c) Store food below ground (pea). 



(d) Digest and absorb from endosperm (corn). 

 Number. 



(a) Monocotyledonous (one cotyledon) (corn). 



(b) Dicotyledonous (two cotyledons) (bean). 



(c) Polycotyledonous (several) (pine). 



(2) Plumule (undeveloped shoot). 

 Development. 



(a) Small if much stored food. 



(b) Large if little stored food. 



(3) Hypocotyl (part below cotyledons). 

 Development. 



(a) Root from lower end. 



(b) Raises cotyledons if it grows up. 

 Endosperm (stored food, may be lacking). 



(a) Why not always present? 



(&) Use to man. 

 Food in seeds. 



May be stored in cotyledons or endosperm. 

 Why stored dry and nearly insoluble. 

 Need of digestion, use of diastase. 



TYPES OF SEED STRUCTURE 



Bean (Dicot., no endosperm). The pod is the fruit. 

 External structure. 

 Shape, colof, etc. 

 Testa. 



Hilum, caused by attachment to pod, used to receive nourishment 



from plant. 



Micropyle, used for exit of hypocotyl (see ridge), 

 used for ingress of pollen (see fertilization). 

 Tegumen, thin, unimportant. 

 Internal structure. 

 Kernel. 



No endosperm (what has become of it?). 

 Cotyledons, two, large and rather thick. 



contain starch and proteid. 



Hypocotyl, finger shaped. In protective pocket. 

 Plumule, moderately developed, two plain leaves, veins, etc. 



