MORPHOLOGY OF THE FLORAL ORGANS 131 



attached for a considerable distance, or may be puncti- 

 form, and is characteristic in shape for some genera. There 

 is often a furrow on this posterior side of the caryopsis in 

 which will be found the hilum. Since the palea is often 

 grown to the caryopsis this must be removed when search- 

 ing for the hilum. 



164. The embryo is straight or nearly so, the plumule 

 directed upward and the young root downward. The 

 corn grain illustrates the general features of all grass 

 embryos. An important organ is the scutellum which is 

 attached to the embryo at the middle and enfolds it, 

 lying against the endosperm on its outer surface. This 

 organ is thought to represent the first leaf or cotyledon. 

 Its function is to absorb the nourishment from the stored 

 food during germination. In large embryos like the corn 

 there may be observed on the sides of the epicotyl, or first 

 joint above the attachment of the scutellum, the begin- 

 nings of lateral or secondary roots. In other genera the 

 rudimentary secondary roots usually appear on the 

 hypocotyl. 



165. The endosperm consists mainly of starch, 

 although there is a considerable amount of oil, which, 

 however, is mainly in the embryo. On the outside within 

 the epidermis is a layer of cells containing aleurone, rich 

 in protein. The stored food is also called albumen by 

 some authors. The endosperm is hard and corneous or 

 mealy according to the density of the starch-contain- 

 ing cells. 



166. The rachilla is the axis of the spikelet. It may be 

 jointed to the pedicel below the glumes (usual in Pani- 

 coideae), or jointed above the glumes (usual in Poa- 

 oidese). It may be continuous (Eragrostis, Fig. 51) or 

 articulated between the florets at maturity (Festuca). 



