MORPHOLOGY OF THE SEEDLING 33 



of the cotyledon to make one think it really a leaf, and it 

 is only by studying many cases that the botanist is enabled 

 to class all cotyledons as leaves in their nature, even if they 

 are quite unable to do the ordinary work of leaves. The 

 study of the various forms which the parts or organs of a 

 plant may assume is called morphology ; it traces the rela- 

 tionship of parts which are really akin to each other, 

 though dissimilar in appearance and often in function. 

 In seeds which have endosperm-) or food stored outside of 

 the embryo, the cotyledons usually become green and 

 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 co 



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. 



45. Classification of Plants by the Number i 



of their Cotyledons. In the pine family the FlG 10 _ Ger 

 germinating seed often displays more than minating pine, 

 two cotyledons, as shown in Fig. 12; in the co ' cot y ledons - 

 majority of common flowering plants the seed con- 

 tains two cotyledons, while in the lilies, the rushes, the 



