HERBACEOUS AND WOODY DICOTYLEDONS 415 



also designated as closed venation, since the veins do not termi- 

 nate in the margin of the leaves, which therefore remain smooth. 

 In dicotyledons the leaves are usually netted-veined, and the 

 veins end free in a rough margin. 



The stems of monocotyledons also have scattered vascular 

 bundles without a cambium layer, while those of dicotyledons 

 form a cylinder in which the cambium adds new tissue to the 

 phloem and xylem layers annually. 



The flowers of the monocotyledons are habitually on the plan 

 of three, while dicotyledonous flowers are more frequently on the 

 plan of four or five parts in a whorl for each set of floral organs. 

 These distinctions between dicotyledons and monocotyledons are 

 graphically illustrated in Fig. 263 and are concisely stated in the 

 summary below. 



SUMMARY 



The embryo of monocotyledons has but one cotyledon and a lat- 

 eral stem tip, while dicotyledons have two cotyledons and a central 

 stem tip. 



The monocotyledons usually have leaves with parallel" veins, and 

 the veinlets do not end free in the margin of the leaf, as in dicoty- 

 ledons, in which netted venation prevails. 



In the stems of monocotyledons the vascular bundles are scattered. 

 In dicotyledons the xylem and phloem form a cylinder inclosing the 

 central pith. 



The flowers of monocotyledons are in threes, but those of dicoty- 

 ledons are in fours or fives. 



