28 



ESSENTIALS OF BOTANY 



leaf-like, as they do, for example, in the four-o'clock, the 

 morning-glory, and the buckwheat; but in the seeds of 

 the grains (which contain endosperm) a large portion of 

 the single cotyledon remains throughout as a thickish 

 mass buried in the seed. In a few cases, as in the pea, 

 there are scales instead of true leaves formed on the first 

 nodes above the cotyledons, and it is only at about the 

 third node above that leaves of the ordinary kind appear. 

 In the bean and some other plants which 

 ,.•'■"•■. in general bear one leaf at a node along 



the stem there is a pair produced at the 

 first node above the cotyledons, and the 

 leaves of this pair differ in shape from 

 those which arise from the succeeding por- 

 tions of the stem. 



37. Classification of Plants by the Number 



of their Cotyledons In the pine family 



the germinating seed often displays more 

 than two cotyledons, as shown in Fig. 12; 

 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 but 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 mo7iocotyledonous plants, 

 which have one seed-leaf. Other important differences 

 nearly always accompany the difference in number of 

 cotyledons, as will be seen later. 



Fig. 12. Germi- 

 nating Pine. 



cOj cotyledons. 



