64 GRASSES OF IOWA. 



Garyopsis or fruit. — The fruit in grasses is called a caryopsis. 

 The thin pericarp or capsule is closely connected with the 

 seed. Physiologically the pericarp takes the place of the 

 testa, being well and strongly developed, while the testa is 

 only feebly so. In general the structure is as follows: The 

 epidermal layers, thinner walled parenchyma and a delicate 

 fibro-vascular bundles. Bran consists of the testa and capsule 

 with the adjacent layer, the nucellus when present and the 

 endosperm. It should also be observed that the pericarp 

 often unites with the bracts, especially palet, but seldom to 

 the llowering glume as in barley. 



Dr. Rodney True* summarizes his work on development of 

 cereals as follows: 



I. In corn, wheat and oats, at the time of fertilization the 

 single ovule is furnished with two integuments which are 

 more or less complete. As development proceeds (1) the 

 outer integument soon disappears; (2) the inner cells of the 

 wall of the ovary are absorbed, in varying proportions; (3) the 

 tissue of the nucellus is absorbed, with local exceptions. 



II. At maturity these remain as seed covering: (1) The 

 external portion of the wall of the ovary in varying propor- 

 tions, forming the pericarp; (2) the inner integument persist- 

 ing in a state of compression. The epidermis of the nucellus 

 also persists, though much compressed. 



III. Late in the development of the fruit, the remaining 

 (inner) integumeut becomes soldered to the adjacent inner 

 cells of the pericarp, forming the fruit correctly described by 

 Mirbel under the name of "cerium "and rechristened by 

 Richard the "caryopsis." 



Zea mays L. In another connection one of us has discussed 

 the structure of Zea. f The pericarp consists of thick-walled epi- 

 dermal cells followed by a layer of variable thicknesses, the 

 walls of which are greatly thickened, with radiating pore 

 canals. The testa is insignificant, the walls are thinner than 

 in pericarp. Remmants of the nucellus may be distinguished 

 in some parts of the seed. This is followed by the endosperm. 

 The aleurone cells are smaller, very different from those 

 underlying it. The starch cells following the aleurone are 

 closely packed and filled with angular starch grains. 



Avena sativa L. In common oats the caryopsis is slightly 



*Bot. Gazette, 18: 214 pL 24-26. 

 +Proc. la. Acad, of Scl. 5: 19fl. 



