1902] NOTES ON THE PHYLOGENY OF LIRIODENDRON 57 • 





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growing in rich soil, or leaves on especially vigorous shoots from 

 old stumps, saplings, etc., show the greatest tendency to varia- 

 tion and large size, and trees in poor soil have smaller acutely 

 lobed leaves, and the leaves on large, mature trees are smaller 

 than those on saplings, and have the lobation reduced almost to 

 cuspidate points. Again, on individual shoots where the supply 

 of nourishment is reduced artificially, or where it is diverted for 

 the formation of flower and fruit, the leaves undergo great reduc- 

 tion in size and lobation, showing a tendency to assume a two- 

 lobed, Liriophyllum-like form. There is nothing particularly 

 new in this view, for we find in Lindley's Introduction to Botany 

 (P- ^36, 1839) the following; ''Lobation [of leaves] is deepest 

 and more pronounced in those individuals of the same species 

 whose vegetation has been least favored by humidity, and the 

 nature of the soil.'' 



Large leaves, affording a larger assimilating area, are of course 

 more advantageous in the performance of the functions of vege- 

 tation than smaller ones, and some of the additional advantages 

 accrumg when these large leaves are lobed instead of simple 

 may be enumerated as follows: The simple leaves are more 

 unwieldy and heavier, and therefore much more easily affected 

 and broken by winds and rain. In the lobed forms the sunlight 



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IS more completely utilized; there is economy of circulation 

 through more direct connection of parts; there are more leaves 

 to a given amount of material, and therefore more active assimi- 

 lating organs. The functional activity of two-lobed leaves, 

 havmg an area equal to that of a single simple leaf, ought to 

 be considerably greater. 



The next stage in the genealogy of Liriodendron which has 

 been preserved is L. giga7iteum Lesq., which is reached by a 

 series of slight changes from the more primitive L. Meekii 

 through constantly enlarging and more lobate forms induced by 

 the environment indicated above. The petiole has become 

 greatly lengthened, and stipules had probably been developed; 

 for, although we have no trace of stipules except in the winged 

 petioles of Liriqphylhim populoides, of the Dakota znd Liriodendron 



