GRASSES OF IOWA. 67 



pericarp follows. It consists of several rows of thick- walled 

 translucent cells, the cavity being very much reduced. The 

 testa is colored brown. The cells are tangentially elongated 

 and the cell-walls are thinner. The nucellus is very much 

 reduced excepting in the groove, where it occurs as thick- 

 walled cells. The endosperm differs in a very marked degree 

 from either that of Triticum or Secale, especially the aleurone, 

 which consists of three to four or exceptionally more rows of 

 cells. The starch cells are much larger and contain large 

 spherical or elliptical starch grains, accompanied by numerous 

 smaller ones. Small protein grains are abundant. 



Structurally there are wide differences between the tribes 

 of the order, very marked in some c'osely allied genera. The 

 pericarp is well developed in such genera as Zea, Arundinaria, 

 and fairly well in Triticum, Secale, Hordeum and Avena. The 

 testa is but slightly developed in most cases, notably so in 

 Festuca, Panicum glabrum, Aristida and Oryza sativa, the pro- 

 tective features being provided for by the glumes surrounding 

 the fruit, or the wall of the ovary. The nucellus is never 

 entirely absent, especially in the groove. It is usually much 

 compressed. In the genera Festuca and Bromus, the cells are 

 large, thick-walled and mucilaginous, and no doubt act as 

 reserve food. The aleurone layer is variable. It is never 

 absent. Of one row of cells in Triticum, Zea, Zizania. The 

 cells are very small in Panicum crus-galli, Aristida, Setaria 

 italica. Of more than one row of cells in Avena, Arrhena- 

 therum, Festuca, Sbud Hordeum vulgare. The starch cells differ in 

 size and contain small spherical or elliptical grains in Sorghum 

 vulgare and Cenchrus tribuloides. Large spherical or some- 

 what elliptical grains occur in Triticum and Hordeum, accom- 

 panied by numerous smaller ones. Small five or six sided 

 grains in Panicum crus-galli, Zea mays, Euchlaena mexicana. 

 This applies in general to the tribe Maydeae and Paniceae. 

 Ceochrus is, however, an exception to the rule. Compound 

 starch grains occur in Zizania, Oryza, Avena, Arrhenatherum, 

 Glyceria, Poa, Phalaris and Arundinaria; most grasses api3ear 

 to have compound grains. The endosperm always contains 

 protein, though much reduced in the starch cells, except in the 

 aleurone layer, where no starch occurs. The starch ctlls next 

 to the endosperm contain more protein than the interior of the 

 endosperm. Fat is also present in small amounts. The com- 



