LOCALIZED STAGES IN DEVELOPMENT. 99 



base of the vine are all trifoliolate (PI. 17, fig. 25, area a) ; those on the old wood are 

 unifoliolate, trilobed (the same figure, area b) ; and those on the new growth are cordate 

 dentate (same figure, area c). There are thus to be seen three zones or localized stages : 

 a, which repeats nepionic characters ; b, which has attained full specific characters ; and c, 

 whicli repeats the second nepionic stage of the 3'oung. Plants var3^ so much in the form 

 of their leaves that Ampelopsis tricuspidata is noteworthy on account of the constancy 

 of the form of its leaves. At the base of plants raised from seed the leaves are always 

 trifoliolate ; when unifoliolate trilobed leaves appear, they mark a sharp line of distinc- 

 tion, and very rarely do more trifoliolate leaves occur; cordate leaves are found only on 

 branches of the current season's growtli. In the diagram (PI. 17, fig. 25), the current 

 season's growth is represented as area c, or on the periphery. Of course in practice new 

 branches may start out from any part of the plant, but where\'er they originate, they 

 are marked by the same type of leaves. When new branches originate from the base 

 within the trifoliolate leaf area a, then cordate leaves immediately succeed trifoliolate 

 leaves, as in seedlings. 



Acer rubrum. The seedling Red Maple, Acer nibrum L. (PI. 17, fig. 28), has two 

 long, strap-shaped cotyledons, rounded distfilly. The first nepionic leaves are opposite, 

 elongate, cordate, acuminate, dentate. They already show indications of the trilobed 

 character of the species in the slightly larger lateral lobes near the base of the leaf. The 

 second pair of leaves is elongate, but differs from the first in the greater develojnnent of 

 the two lateral lobes, rendering the leaf trilobate ; but the median lobe is markedly 

 elongate. The same features, though in slightly varying degrees, are characteristic of 

 seedlings of Acer saccharum Marsh, A. spicattim L., A. platanoides L., and A. pseudo- 

 platanua L. In Acer pennsylvanicum L., the first pair of nepionic leaves is simpler than 

 in the species noted, being ovate, dentate, with no evidence of a trilobed character as 

 described by Mr. Deane ('96). This species in its development is structurally the most 

 primitive species of maple seen. 



As the Red Maple grows older, the trilobate character becomes more marked, and 

 two additional lateral lobes may appear on the proximal border of the leaves. The fea- 

 ture of change is the relative shortening of the median and enlargement of the lateral 

 lobes. The leaf of the adult tree is trilobed or slightly five-lobed (PI. 17, fig. 29, leaf 1). 

 Individual trees with trilobed leaves may properly be considered more pilmitive in char- 

 acter than those with five-lobed leaves, as they bear a closer resemblance to the young 

 and fossil forms; also they are less differentiated on the proximal portion. 



In the Red Maple, young suckers from the base (PL 17, fig. 27), or other part of the 

 tree, have trilobed leaves in which the median lobe is elongate, as in the seedling. In 

 vigorous shoots, or young leaves at the tips of branches (PI. 17, figs. 26, 29), or in the 



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