Seedling Anatomy of Certain Sympetalae. II. 329 
4. It is held (a) that the evolution of the vascular structures of seed- 
lings is probably not an extremely slow process; but that (b) tetrarchy 
and diarchy have probably been interchanged several times during the 
evolution of Angiosperms. 
5. It seems probable that physiological factors are not sufficient to 
account for all the structures found in seedlings. 
6. There are many exceptions to the rule that size of seedling is 
correlated with the type of structure. 
Bibliography. 
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(A more complete list will be found in the previous paper (7).) 
