1902] NOTES ON THE PHYLOGENY OF LIRIODENDRON 51 



the number of described forms of Liriodendron, and so need- 

 lessly encumber the synonymy. 



In comparing the ancient types of Liriodendron with the 

 modern varieties of Z. Tulipifera, the purpose is to establish the 

 fact that those ancient forms of leaves which were simple, or 

 with unnotched apices, or with winged petioles, and which some 

 authorities are inclined to exclude from Liriodendron, are 



undoubtedly correctly identified as primitive forms of that 

 genus. 



THE EVOLUTION OF LIRIODENDRON. 



Following Holm, we would consider the primitive ancestral 

 type of Liriodendron to have been a simple, Magnolia-like leaf ; 

 for not only do all the modern relatives of Liriodendron have 

 such leaves (Magnolia, Anonaceae, etc.), but there is a progres- 

 sive simplification and reduction in lobation as we proceed back 

 in time, the most primitive known forms having ovate or oblong 



:)Ie leaves [Jig, j) , VVe find in the growth of our modern L. 



ipifera a parallel development, from the youngest entire or 



merely notched forms to those of the mature, typically lobed 

 leaves. 



Generally speaking, no significance can be attached to the 

 form of the cotyledons ; but in this case they represent almost 

 exactly the form we imagine to have been assumed by the 

 primitive Liriodendron leaf, which grew in the early Cretaceous 

 01" Jura-Cretaceous. (See Torreya 2: pL i. figs. 6-8, 1902.) 

 We picture this ancestor as a tree with simple, ovate or lanceo- 

 late leaves, short petioled and without stipules or bud-scales. 

 The vernation of the leaves was probably conduplicate, as in 

 the existing Magnolia, it being obviously improbable for it 

 to have teen reflexed in the ancestor of short-petioled leaves 

 such as those of Liriodendron simplex and L. primaevum. We 

 consider that this entire, oblang form of leaf, tapering at 

 both ends to a blunt point, was succeeded by a series of 

 forms ranging from Liriodendropsis aiigustifolia Newb. at the 

 one extreme, through Liriodendron simplex Newb., L. primaevtim 



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