290 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Much has been written on its morphological nature. Arber (1934) 

 considers that the scutellum and coleoptile jointly constitute the 

 cotyledon, the coleoptile representing the cotyledonary sheath. 

 Others contend that the coleoptile is the true cotyledon and that 

 the scutellum is a lateral outgrowth of the young axis. Avery 

 (1930), who has made a thorough study of the comparative anatomy 

 and morphology of the embryos and seedlings of maize, oat, and 

 wheat, interprets the scutellum as the cotyledon; the coleoptile as 

 the second leaf; and the elongated structure between the cotyledon 



Fig. 164. Development of embryo in Poa annua. (Redrawn after Soueges, 1924b.) 



and the coleoptile, sometimes called the "mesocotyl," as the first 

 internode. 



It is to be noted that, on the side which is in contact with the 

 endosperm, the cells of the scutellum frequently elongate to form 

 finger-like processes, which project into the endosperm and probably 

 serve for the absorption of food from the latter. 



MODIFICATIONS OF SUSPENSOR 



In the above account of the principal types of embryonal develop- 

 ment in the dicotyledons and monocotyledons, the main emphasis 

 was on the embryo proper and little attention was paid to the sus- 

 pensor. This is because in the majority of angiosperms the sus- 

 pensor has no special function except that of pushing the embryo 



