THE PAETS OF THE SEEDLING. 



17 



the cotyledons, and the leaves of this pair differ in shape 

 from those which arise from the succeeding portions of the 

 stem. 



21. Classification of Plants hy the JSfum.ber of 

 their Cotyledons. — In the pine family the germi- 

 nating seed often displays more than two coty- 

 ledons, as shown in Fig. 6; in the majority of 

 common flowering plants the seed contains two 

 cotyledons, while in the lilies, the rushes, the 

 sedges, the grasses, and some other plants there 

 is bui; one cotyledon. Upon these facts is based 

 the division of most flowering plants into two 

 great groups : the dicotyledonous plants, which have 

 two seed-leaves, and the monocotyledonous plants, 

 which have one seed-leaf. Other important differ- 

 ences constantly accompany the difference in 

 number of cotyledons, as will be seen later. 



Fig. 6. — Ger- 

 minating 

 Pine. 



c, cotyledons. 



