570 THE STRUCTURE OF ECONOMIC PLANTS 



is subdivided into an outer and inner zone, and the innermost 

 layer or epidermis which is highly pigmented, giving color to the 

 mature seed. (Fig. 197, C.) As the seed enlarges, the number 

 of parenchymatous cells of the outer zone is increased by many 

 cell divisions. 



The walls of the outer epidermis develop thickenings which 

 are initiated on the inner walls and at the base of the lateral walls. 

 (Fig. 197, D.) While still in the fruit, the epidermal cells of the 

 partially mature seed show longitudinal bands or thickenings 

 that are more or less localized at the angles of the cells; and these 

 continue to the external wall, forming a large irregular network 

 or mesh. (Fig. X97, E, F.') During the final stages of maturation, 

 the portions of the lateral wall between the longitudinal bands 

 are split, and the external wall also disappears. In this manner 

 the bands are isolated from one another and form long "hairs" 

 or scales that cover the outer surface of the seed at maturity. 

 (Fig. X97, C) The basal portions of the bands are sinuous and 

 irregular, being thickest at the angles from which the "hairs" 

 arise. (Fig. ^97, B.) 



While this development is taking place, there is a gradual 

 resorption of the intermediate zones. This is initiated in the 

 inner zone of parenchyma and continues progressively until 

 maturity. Nothing is left of the intermediate parenchyma except 

 a crushed membranous layer which with the inner layer gives 

 color to the seed. (Fig. x^-/, C-C) The haustorial or digestive 

 cells of the innermost layer are rectangular in transection and 

 polygonal as seen in surface view. 



Development of the Seedling. — Although variation in the 

 size of the seed may not proportionately affect the yield of fruit, 

 the percentage of germination is much lower in lots of light seed 

 as compared with lots of larger, heavier seed. Under greenhouse 

 conditions, the seeds germinate rather rapidly; and, by the seventh 

 day, produce a slender tap root an inch or more in length with 

 numerous root hairs. The hypocotyledonary arch emerges from 

 the soil, and this is followed by liberation from the seed coat of 

 the slender linear or lanceolate cotyledons which function as the 

 first photosynthetic leaves. (Fig. X98, B-F.') 



The Primary Root. — The primary root resembles other 

 solanaceous forms (potato, tobacco, eggplant) in all essential 

 details. It has a diarch protostele and the two groups of primary 



