THE AMERICAN BOTANIST 



Fig 2. 



though mature and appearing at a later period of growth of 

 the plant, has not developed i)eyond the stage represented by 

 the cotyledon. On the other hand, its great difference from 



the normal leaf of this variety of 

 morning-glory may be seen by compar- 

 ing it with figure 3. 



In this case a single leaf only was 

 involved, though several similar leaves 

 were afterwards found on different 

 plants. Sometimes, however, all the 

 leaves of a given tree or plant are thus 

 retarded As is well known, the first 

 leaves put forth by the seedling sassa- 

 fras are the simple, non-lobed forms, 

 the lobed forms appearing later. This 

 is also true of the individual branches, 

 on each of which the lower leaves are simple, while those of 

 the median portion, and some- 

 times those of the upper portion 

 also are lobed, though frequently 

 the uppermost zone of leaves is 

 simple. It therefore appears 

 reasonable to consider such simple 

 leaves as may be found occupying 

 the median portion of the branch 

 as retarded forms. A splendid 

 example of this kind of retarda- 

 tion is a sassafras tree growing 

 in Bronx Park, New York City. 

 It is between ten and fifteen 

 feet high and for two seasons has been practically covered 

 with simple leaves. Last season less than half a dozen lobed 

 forms could be seen, while the season before none were found. 



