LOCALIZED STAGES IN DEVELOPMENT. 101 



of the serrations on the sides being strongly marked, so that the leaf strikingly resem- 

 bles the first nepionic leaves of the seedling of the Red Maple (Fig. 28, leaf 1). It is 

 also quite like the simplest of the fossil maples, as Acer indtvistim Web., of the late 

 Ci'etaceous (Laramie) and Tertiary'. All the leaves of this species are similar, no vari- 

 ation having been observed. It is a distinctly archaic type in its form. 



Acer tartaricum L. var. gbuiale Maxim., from Jesso, Japan, Coll. Dr. H. Mayr, 

 presents interesting features. On the proximal end of the branchlets (PI. 17, fig. 33) 

 are two bluntly oval, very slightly serrate leaves; similar leaves occur on many speci- 

 mens seen in the herbarium of the Arnold arboretum. Beyond this single pair of leaves 

 all the leaves are of a strikingly different form (Fig. 33); they are elongate, slightly 

 trilobed, with serrate margins. Individual leaves show considerable variation in the 

 trilobed character, some being less, others a little more, deeply trilobed than the leaves 

 figured, which represent a fair average. This type of leaf bears considerable resem- 

 blance to the weakly trilobed leaves seen in the second pair of leaves and in the later 

 leaves of young Red Maples (Fig. 28) and other species. It may, therefore, in the 

 character of these leaves be considered a primitive type but more advanced structurally 

 than Acer crataegifol'mm. In regard to the two oval nearly entire leaves seen at the 

 base (PL 17, fig. 33), they may be considered a localized reversion to a simpler type, 

 and as such may be compared to Gledltschia trlacanthos in which the proximal leaves 

 are once compound, the distal being more specialized and twice compound. (See p. 102.) 



Fossil Maples. In Acer indlvisum Web., of the late Cretaceous and Tertiary, 

 we find a type in which the leaves are either without lobes, or with two slight lobes quite 

 similar to the first nepionic leaves of Acer ruhrum and A. j>seudo-iilatanus. In the Creta- 

 ceous and Tertiary maples the species are almost universally trilobed, and an elongate 

 character of the median lobe is of frequent occurrence, as in Acer trilohatum A. Br. and 

 A. dec%2ylens Heer. The trilobed character of maples finds, then, an expression in many 

 fossil species and primitive living species, as Acer crataegifolium and A. ruhrum. An 

 elongate trilobed form is seen in some fossil species, in the young of all species observed, 

 and in vigorous growths, and leaves of terminal branches of Acer ruhrum and many 

 other species. Acer pennsylvanicum forms a partial exception to this rule, because the 

 first pair of nepionic leaves shows no trilobate character, tliis feature being developed in 

 later growth. Species such as the Sugar, White, and Norway Maples, besides other 

 features are differentiated by having two lobes added to the proximal end of the leaf, 

 but in the young and degradational leaves they show the more primitive trilobed char- 

 acter. 



Negundo aceroides. In the Ash-leaved Maple, Negundo aceroldes M., the seedling 

 has simple trilobed leaves. My material is imperfect, and first nepionic leaves and coty- 



