538 



WEED FLORA OF IOWA 



3. Fiber Layer (f). The fibers of this layer are 15-40a* broad 

 and are parallel to the curved axis of the seed. Seen in cross 

 section, this layer is thickest in the ribs, the walls throughout 

 being distinctly thickened and stratified. In surface view they 

 are rendered more distinct by chlorzinc iodine. 4. Cross-Cells (q). 

 The fourth layer consists of moderately thick-walled, transversely 

 elongated, pointed cells arranged side by side in rows. The walls 

 are impregnated with brown material. 5. Netted-Cells (n) . Ow- 

 ing to the netted-veined, colorless walls and the presence of deep 

 brown contents, these cells are particularly striking. They are 

 arranged transversely and often side by side in rows. The cell 

 contents are insoluble in alkali and do not give the tannin re- 

 action. Some authors designate the cells of this layer "Pigment 

 cells," notwithstanding the fact that in the white poppy they do 

 not contain pigment. Meyer, Tschirch and Oesterle, Vogl, and 

 Hanausek describe an inner layer of thin-walled cells, but I am 

 unable to find such a layer except in the vicinity of the hilum. 



Fig. 415. Poppy seed. Testa in surface view. Significance of letters same as 



in Fig 414. pig, pigment. X 160. 



(After Winton, Conn. Agr. Exp. Sta.) 



The Endosperm (E) contains aleurone grains up to 3^ in 

 the outer layers and 7a* in the inner layers, each grain containing 

 several globoids and crystaloids. 



Embryo. — In the cotyledons there is only one layer of palisade- 

 cells and these cells are only slightly elongated. The aleurone 

 grains are like those of the endosperm. 



