TRITICUM 1 01 



1. Ovary wall or pericarp, of several cell layers. 



2. Testa, two layers of inner integument. 



3. Nucellus. 



4. Aleurone layer, outermost layer of endosperm. 



5. Starchy endosperm. 



Ovary Wall or Pericarp. — The pericarp of the mature 

 grain is composed of several layers of highly compressed 

 cells, the original cavities of which can scarcely be distin- 

 guished. The walls are thickened, cuticularized and lignified. 

 The chlorophyll-bearing layer, now colorless, is below these 

 layers. Its cells are marked by numerous narrow trans- 

 verse pits. The outside wall of chlorophyll cells is thin, while 

 the inside wall, next to the integument, is thick. In tan- 

 gential view, chlorophyll-bearing cells appear strongly 

 thickened, rounded at the ends, and closely fitting, thus 

 leaving no intercellular spaces. In rye, these same cells as 

 seen in tangential section are pointed at the ends. 



The grains of spelt, emmer, and einkorn have the palet and 

 lemma attached, and in these the pericarp is more weakly 

 developed than in the types of wheat with naked grains. In 

 all wheats, the layers of the grain, both fruit and seed, are 

 much thinner at the embryo end than in the other parts of 

 the fruit. It is known that the greatest amount of absorp- 

 tion of water takes place at the embryo end. 



Testa (episperm). — It has been noted that, in the develop- 

 ing wheat grain, the testa is composed of two integuments of 

 two layers each. In the ripening process, the outer integu- 

 ment is entirely absorbed, so that in the mature grain the 

 testa consists of two rows of cells, belonging to the inner 

 integument. The walls are slightly lignified. 



The coloring matter of the grain is found in the inner layer 

 of the testa. It is of two kinds, pale yellow and orange 



