522 



WEED FLORA OF IOWA 



Palet. — The two-keeled palet is about the same size as the flower- 

 ing glume, but is of a thinner texture, owing to the absence of a 

 well developed hypoderm layer. The Outer Epidermis is much the 

 same as that of the flowering glume, except that it is barbed on 

 the keels with rigid thornlike hairs 150 or less in length, as is 

 shown in Fig. 3 by Moeller. 



Fig. 400. Darnel. 



Keel of palet showing outer epidermis with hair h, and 



hypoderm fibers f. X 160. 

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



The Pericarp (F). — Consists of four coats, of which only two, the 

 epidermis and cross-cells, are fully developed. 1. Epidermis (ep). 

 Cross sections of the mature seed show that this layer consists of 

 collapsed, moderately thick-walled cells, which are best studied 

 after heating with potash. Seen in surface view, the cells at the 

 apex of the seed are nearly isodiametric, but at other parts are 

 elongated. The walls are indistinctly beaded. 2. The Mesocarp (m) 

 is not developed on all parts of the seed, but is conspicuous on the 

 angles. The cells vary greatly in shape and size, some being ir- 

 regularly isodiametric, others transversely elongated, resembling the 

 cells of the next layer. 3. Cross-Cells (q). Especially striking are 

 the cells of this layer, which resemble the cross-cells of barley. As 

 has been noted by Moeller, the radial walls appear indistinctly 

 beaded, but this is evident only under favorable conditions. 

 4. Tube-Cells, spongy-parenchyma, and various intermediate forms, 

 make up the interrupted inner layer of the pericarp. 



Testa (S). — The cells are for the most part elongated and are 

 often diagonally arranged with reference to the axis of the fruit. In 



