590 THE STRUCTURE OF ECONOMIC PLANTS 



adheres to the seeds. It becomes firmly attached to the seed coat, 

 but can be separated from dry seeds as a transparent colorless skin. 



The Seed. — The large, flat, ovate seeds are pointed at one 

 end; and vary so definitely in shape, color, margin, and the scar 

 formed at the hilum that Russell (33) has devised a key to separate 

 the three species based on these characters. 



The structure of the seed coat has been investigated by Barber (2.), 

 Kondo (2.4), Yasuda (42.), and Fickel (10). Kondo investigated 

 that of C. moschata and the other accounts described varieties of 

 C. Pepo. The seed coat is comprised of five distinct layers of tissue 

 which develop as parts of the two integuments of the anatropous 

 ovule. The outer integument produces the three outermost layers 

 of the seed coat, and a part of the fourth layer; while the remainder 

 of the coat is derived from the inner integument. 



The outer epidermis (i) is made up of prismatic cells which 

 form a compact layer devoid of intercellular spaces. The cells 

 are elongated radially, and those lying at the border form a ridge 

 in which the cells are several times as long as those on the flattened 

 lateral surfaces of the seed. The outer walls of these cells are 

 thickened, but there is little or no cuticle. The radial walls are 

 very thin with characteristic strands of cellulose thickening which 

 extend from the base of the cell and branch frequently toward the 

 outer wall. (Fig. 308, A.") 



The subepidermal layer Ql) is made up of small, thick-walled, 

 much pitted, polygonal cells that are somewhat elongated. There 

 are no intercellular spaces in this zone, which is three to five 

 layers in thickness except at the margin of the seed where the 

 number increases. The sclerenchymatous region (3) gives firmness 

 to the seed coat, and is one cell layer in thickness except at the 

 margin of the seed where it may be two or three. The longitudi- 

 nally elongated cells are arranged in rows end to end; and in surface 

 view, the very thick walls appear sinuous with infoldings that 

 overlap one another. 



The parenchymatous zone (4) consists of three distinct layers. 

 The outer one is made up of small pitted cells which lie adjacent 

 to the sclerenchyma and have no intercellular spaces. The inter- 

 mediate region is two layers in thickness and is characteristic of 

 the genus. The intercellular spaces are very large, forming 

 cavities into which the cells project, and the cells are somewhat 

 stellate with walls that have reticulate thickenings. The inner 



