X50 THE STRUCTURE OF ECONOMIC PLANTS 



and may be easily duplicated in controlled environments in green- 

 houses. 



In Europe, the biennial method is used. It consists in planting 

 the seed in July or August and digging the small beets before frost. 

 The roots are then stored in out-of-door pits over the w^inter where 

 the lovv^ temperatures condition the roots for seed stalk production. 

 In the spring, the roots are replanted, seed stalks develop, and the 

 seed is harvested in July. 



The Seed. — The mature seed is a flat, shiny, reddish-brow^n 

 structure which ranges from 1.5 to 3 mm. in diameter, and is 

 approximately 1.5 mm. in thickness. The seed coat has two 

 integuments, the curved embryo within completely surrounds the 

 perisperm, and a single layer of endosperm encloses the distal 

 portionof the primary root. (Fig. 119.) Each of the integuments 

 consists initially of two cell layers, except near the chalaza where 

 they are more numerous; but in the mature seed coat, only three 

 remain, since the outermost layer of the inner integument dis- 

 integrates during the development of the seed. The cells of the 

 outer integument are at first undifferentiated, but later the outer 

 wall becomes thickened and is covered with an extensive cuticle. 

 The second layer of the outer integument is comprised of small 

 cells with dense contents, and the individual cells are separated 

 from one another by small intercellular spaces. The layers of the 

 inner integument are at first meristematic; but, as maturation 

 of the seed proceeds, the outer layer remains small, the nuclei dis- 

 integrate and the cells are obliterated. Meanwhile, the cells of 

 the inner layer of the inner integument enlarge and the walls 

 become delicately sculptured. A thick cuticle is laid down 

 between the inner integument and the nucellus which, according 

 to Bennett and Esau (6), may be recognized by microchemical 

 tests when the embryo consists of approximately nine cells. They 

 point out that the cuticle is lacking in the chalazal region where 

 the phloem approaches the perisperm, so that a "passage region" 

 is formed through which materials can move into the latter. 

 When the seed has reached maturity, the walls of the cells in this 

 zone also become cutinized or suberized, sealing off the embryo 

 and perisperm. 



Artschwager (x) reports that "the cells of the outer integument 

 contain starch and there is an extensive tannin deposit in both 

 integumentary layers." The embryo is filled with albuminous 



