108 HOBERT TRACY JACKSON ON 



nepionic leaves are arranged alternately on the stem. The first nepionic leaves are small, 

 ovalh- rouiiikMl ; later leaves retain the same oval outline but increase greatly in size. In 

 the specimen figured the sixth leaf from the base shows slight marginal undulations, which 

 may be the first appearance of lobes ; but such do not often occur until considerably later. 

 In PL 19, fig. 50, is shown the upper part of an older seedhng. The lower part of this 

 specimen had only oval leaves, as in Fig. 49, but the upper part bears three leaves with 

 two or three lobes. In seedlings the lobed leaves occur in the upper part or later growth 

 only ; but in this same area some ovate leaves are not infrequently associated with the 

 lobed leaves. In the adult tree the leaves are borne on short branchlets of the current 

 season's growth. At the base or proximal portion of such branches (PL I'.i, fig. -jl), all 

 the leaves are ovally rounded, ovate or obovate, as in the young seedling. At the upper 

 part of the branch, however, lobed leaves are often developed, although many branches 

 bear no lolled leaves. Amongst the lobed leaves of the upper part of the branch, ovate 

 leaves may or may not develop, this feature being variable. Each branch of the adult, 

 therefore, which bears lobed leaves, repeats the features characteristic of the seedhng, 

 having oval leaves proximally and leaves with two or three lobes distally, with or without 

 associated oval leaves. Lobed leaves are much more common in plants up to five or six 

 feet high than in adidts. As branches of adults bear oval leaves throughout the branch 

 or on the proximal part, when distal leaves are lobed, therefore oval leaves are the domi- 

 nant type, the lobed leaves the exceptional. Professor Ward ('88) maintains the same 

 view. The Sassafras suckers freely from the root, and such suckers repeat the form of 

 the seedling so closely that often they cannot be distinguished until the root is examined. 

 The Sassafras is abundantly represented in the Dakota group (Cretaceous) of this 

 country. These old species (Lesquereux, '91) are two- or three-lobed, similarly to the lobed 

 condition of modern Sassafras sassafras in the later growths of seedUngs or occasional 

 leaves at the tips of branches of adults. The fact that seedUngs start with entire leaves 

 and later acquire lobed leaves like the earliest fossil representatives seems difficult to 

 harmonize with the usual condition, Avhere the first leaves are like the primitive or ancient 

 types, and later leaves are different, being more specialized, as in Liriodendron, White Ash, 

 and Platanus. They may be less specialized, however, as in Ampelopsls trkuspidata and 

 Fraxinm anomala. Granting that in adult Sassafras sassafras the oval leaves are by 

 far the most numerous, also that lobed leaves when existent are pretty definitely limited 

 to a certain portion of the branch, the end, we may fairly assume that the lobed leaves 

 are not the typical leaf of the species, but are localized reversions of frequent occurrence. 

 By the principle of acceleration of development stages are shoved back earlier and earlier, 

 so that we expect to find ancestral stages in the very young. In this species, however, 

 the species features (oval leaves) are found in the young seedling (PL 19, fig. 49), and 



