18G 



MANUAL OF BOTANY 



and the embryo becomes differentiated histologically in the 

 same way. The young stem is derived from the upper cell 

 of the two resulting from the first division of the hypophysis, 

 and as it assumes its form it turns out laterally from below the 

 cotyledon. 



This division of the Phanerogamia includes the two classes 

 of Monocotyledons and Dicotyledons, which are distinguished 

 from each other by the following points : — 



Fig. 936. 



FUj, 9oG. Successive stages iu development of the embryo of Brassica. 



After Kuy. 



Monocotyledons. — The embryo has a single cotyledon, which 

 is placed at its apex, while the plumule arises laterally ; the 

 flower is usually trimerous ; the vascular bundles do not con- 

 tain cambium and are small and arranged in a scattered 

 naanner in the stele ; the foliage leaves usually have parallel 

 venation. 



Dicotyledons. — The embryo has two cotyledons, between 



