THREE EXAMPLES OF RETARDED DEVELOP- 

 MENT AMONG LEAVES. 



By Edwin W. Humphreys. 



VARIATION in leaf form is an exceedingly interesting 

 field for study. Even a cursory examination of a plant 

 will often reveal some remarkably shaped leaves. Besides 

 what may be called normal or expected differences in shape, 



as in the case of the sassafras, mulberry and others, there are 

 often to be found strange and unusual forms. It is to some 

 of these peculiar forms that attention is here directed. 



The most remarkable of the three examples occurred on 

 the common garden morning-glory. While removing some 

 dead and withered leaves from certain plants in my garden, 

 the leaf illustrated (fig. 1) was found. To one familiar with 

 the seedling morning-glory of this variety the cotyledons are 

 irresistibly called to mind. The figure ( fig 2 ) shows the shape 

 and nervation of the cotyledon, so that the reader may com- 

 pare it with the later, unusual leaf and note their essential 

 similarity. It is because of this similarity that the large leaf 

 is looked upon as a retarded or atavistic form ; one which, 



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