LACTUCA SATIVA 



633 



of the integument are disorganized, and the inner walls of the 

 laterally placed epidermal cells may invest the endosperm so 

 closely that they appear to be a part of it. Borthwick and Robbins 

 determined that this translucent integumentary membrane is 

 continuous and semi-permeable. 



As the akene matures, the ribs of the pericarp develop. (Fig. 

 330, A, JB.) These are rather equally spaced and consist of thick- 

 walled sclerenchymatous fibers which are pitted and lignified. 

 cot 



■ S c 



l-vas bu 



fr c-^ 



^ al gr 



Fig. }}o. a, transection of akene; B, transection of portion of fruit coat of light-colored 

 akene ; C, same of dark fruit : al gr, aleurone grain ; cot, cotyledon ; end, endosperm ; /;• c, 

 fruit coat; rb, rib; s c, seed coat; vas bu, vascular bundle. (Redrawn after Kondo, Ohara 

 Institute.) 



The remainder of the pericarp in the mature akene is only one or 

 two cells in thickness since the other cells of the parenchymatous 

 portion of the fruit coat become disorganized. There is a wide 

 range in the color of the fruit from buff to dark brown and from 

 light gray to carbon gray or black. This difference is due in part 

 to the presence or absence of pigment in the epidermis of the 

 pericarp. In the dark-colored fruits, the outer epidermis is filled 

 with a dark brown pigment which is entirely lacking in the light- 

 colored fruits. (Fig. 330, B, C) 



The cells of the mature integument are much crushed and par- 

 tially disintegrated, but the outer epidermis may persist as a 



