122 



HISTOLOGY OF THE GRAIN 



[oh. 



coats, differing in the number of layers and in the micro- 

 scopic characters of the cells, some of which characters 

 can be employed in diagnoses. (Fig. 39.) 



Secondly, the great mass of the " grain " internally is 

 composed of delicate cells filled in most cases with starch- 

 grains, the sizes, shapes and arrangement of which can 

 also be employed for diagnoses — e.g. the compound grains 

 of the Aveneae and Festucese are different from the simple 

 polyhedral or rounded grains of the Andropogoneae and 



Fig. 39. Transverse section (highly magnified) through a, grain of 

 Urachypodium pinnatum taken about half-way up. 1, epidermis ; 

 2, pericarp; 3, remains of the true seed-eoat; 4, vascular bundle; 

 5, remains of nueellus; P, epidermis of nucellus; G, aleurone 

 layer: remarkable in being several cells thick; E, endosperm. 

 Harz. 



Maydeae, and some races of Maize have sugar and soluble 

 starch instead of grains of the latter. 



